Theories, Hypotheses, and Laws: Definitions, examples, and their roles in science
by Anthony Carpi, Ph.D., Anne E. Egger, Ph.D.
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Did you know that the idea of evolution had been part of Western thought for more than 2,000 years before Charles Darwin was born? Like many theories, the theory of evolution was the result of the work of many different scientists working in different disciplines over a period of time.
A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and is logical, testable, and predictive.
As new evidence comes to light, or new interpretations of existing data are proposed, theories may be revised and even change; however, they are not tenuous or speculative.
A scientific hypothesis is an inferred explanation of an observation or research finding; while more exploratory in nature than a theory, it is based on existing scientific knowledge.
A scientific law is an expression of a mathematical or descriptive relationship observed in nature.
Imagine yourself shopping in a grocery store with a good friend who happens to be a chemist. Struggling to choose between the many different types of tomatoes in front of you, you pick one up, turn to your friend, and ask her if she thinks the tomato is organic . Your friend simply chuckles and replies, "Of course it's organic!" without even looking at how the fruit was grown. Why the amused reaction? Your friend is highlighting a simple difference in vocabulary. To a chemist, the term organic refers to any compound in which hydrogen is bonded to carbon. Tomatoes (like all plants) are abundant in organic compounds – thus your friend's laughter. In modern agriculture, however, organic has come to mean food items grown or raised without the use of chemical fertilizers, pesticides, or other additives.
So who is correct? You both are. Both uses of the word are correct, though they mean different things in different contexts. There are, of course, lots of words that have more than one meaning (like bat , for example), but multiple meanings can be especially confusing when two meanings convey very different ideas and are specific to one field of study.
- Scientific theories
The term theory also has two meanings, and this double meaning often leads to confusion. In common language, the term theory generally refers to speculation or a hunch or guess. You might have a theory about why your favorite sports team isn't playing well, or who ate the last cookie from the cookie jar. But these theories do not fit the scientific use of the term. In science, a theory is a well-substantiated and comprehensive set of ideas that explains a phenomenon in nature. A scientific theory is based on large amounts of data and observations that have been collected over time. Scientific theories can be tested and refined by additional research , and they allow scientists to make predictions. Though you may be correct in your hunch, your cookie jar conjecture doesn't fit this more rigorous definition.
All scientific disciplines have well-established, fundamental theories . For example, atomic theory describes the nature of matter and is supported by multiple lines of evidence from the way substances behave and react in the world around us (see our series on Atomic Theory ). Plate tectonic theory describes the large scale movement of the outer layer of the Earth and is supported by evidence from studies about earthquakes , magnetic properties of the rocks that make up the seafloor , and the distribution of volcanoes on Earth (see our series on Plate Tectonic Theory ). The theory of evolution by natural selection , which describes the mechanism by which inherited traits that affect survivability or reproductive success can cause changes in living organisms over generations , is supported by extensive studies of DNA , fossils , and other types of scientific evidence (see our Charles Darwin series for more information). Each of these major theories guides and informs modern research in those fields, integrating a broad, comprehensive set of ideas.
So how are these fundamental theories developed, and why are they considered so well supported? Let's take a closer look at some of the data and research supporting the theory of natural selection to better see how a theory develops.
Comprehension Checkpoint
- The development of a scientific theory: Evolution and natural selection
The theory of evolution by natural selection is sometimes maligned as Charles Darwin 's speculation on the origin of modern life forms. However, evolutionary theory is not speculation. While Darwin is rightly credited with first articulating the theory of natural selection, his ideas built on more than a century of scientific research that came before him, and are supported by over a century and a half of research since.
- The Fixity Notion: Linnaeus
Figure 1: Cover of the 1760 edition of Systema Naturae .
Research about the origins and diversity of life proliferated in the 18th and 19th centuries. Carolus Linnaeus , a Swedish botanist and the father of modern taxonomy (see our module Taxonomy I for more information), was a devout Christian who believed in the concept of Fixity of Species , an idea based on the biblical story of creation. The Fixity of Species concept said that each species is based on an ideal form that has not changed over time. In the early stages of his career, Linnaeus traveled extensively and collected data on the structural similarities and differences between different species of plants. Noting that some very different plants had similar structures, he began to piece together his landmark work, Systema Naturae, in 1735 (Figure 1). In Systema , Linnaeus classified organisms into related groups based on similarities in their physical features. He developed a hierarchical classification system , even drawing relationships between seemingly disparate species (for example, humans, orangutans, and chimpanzees) based on the physical similarities that he observed between these organisms. Linnaeus did not explicitly discuss change in organisms or propose a reason for his hierarchy, but by grouping organisms based on physical characteristics, he suggested that species are related, unintentionally challenging the Fixity notion that each species is created in a unique, ideal form.
- The age of Earth: Leclerc and Hutton
Also in the early 1700s, Georges-Louis Leclerc, a French naturalist, and James Hutton , a Scottish geologist, began to develop new ideas about the age of the Earth. At the time, many people thought of the Earth as 6,000 years old, based on a strict interpretation of the events detailed in the Christian Old Testament by the influential Scottish Archbishop Ussher. By observing other planets and comets in the solar system , Leclerc hypothesized that Earth began as a hot, fiery ball of molten rock, mostly consisting of iron. Using the cooling rate of iron, Leclerc calculated that Earth must therefore be at least 70,000 years old in order to have reached its present temperature.
Hutton approached the same topic from a different perspective, gathering observations of the relationships between different rock formations and the rates of modern geological processes near his home in Scotland. He recognized that the relatively slow processes of erosion and sedimentation could not create all of the exposed rock layers in only a few thousand years (see our module The Rock Cycle ). Based on his extensive collection of data (just one of his many publications ran to 2,138 pages), Hutton suggested that the Earth was far older than human history – hundreds of millions of years old.
While we now know that both Leclerc and Hutton significantly underestimated the age of the Earth (by about 4 billion years), their work shattered long-held beliefs and opened a window into research on how life can change over these very long timescales.
- Fossil studies lead to the development of a theory of evolution: Cuvier
Figure 2: Illustration of an Indian elephant jaw and a mammoth jaw from Cuvier's 1796 paper.
With the age of Earth now extended by Leclerc and Hutton, more researchers began to turn their attention to studying past life. Fossils are the main way to study past life forms, and several key studies on fossils helped in the development of a theory of evolution . In 1795, Georges Cuvier began to work at the National Museum in Paris as a naturalist and anatomist. Through his work, Cuvier became interested in fossils found near Paris, which some claimed were the remains of the elephants that Hannibal rode over the Alps when he invaded Rome in 218 BCE . In studying both the fossils and living species , Cuvier documented different patterns in the dental structure and number of teeth between the fossils and modern elephants (Figure 2) (Horner, 1843). Based on these data , Cuvier hypothesized that the fossil remains were not left by Hannibal, but were from a distinct species of animal that once roamed through Europe and had gone extinct thousands of years earlier: the mammoth. The concept of species extinction had been discussed by a few individuals before Cuvier, but it was in direct opposition to the Fixity of Species concept – if every organism were based on a perfectly adapted, ideal form, how could any cease to exist? That would suggest it was no longer ideal.
While his work provided critical evidence of extinction , a key component of evolution , Cuvier was highly critical of the idea that species could change over time. As a result of his extensive studies of animal anatomy, Cuvier had developed a holistic view of organisms , stating that the
number, direction, and shape of the bones that compose each part of an animal's body are always in a necessary relation to all the other parts, in such a way that ... one can infer the whole from any one of them ...
In other words, Cuvier viewed each part of an organism as a unique, essential component of the whole organism. If one part were to change, he believed, the organism could not survive. His skepticism about the ability of organisms to change led him to criticize the whole idea of evolution , and his prominence in France as a scientist played a large role in discouraging the acceptance of the idea in the scientific community.
- Studies of invertebrates support a theory of change in species: Lamarck
Jean Baptiste Lamarck, a contemporary of Cuvier's at the National Museum in Paris, studied invertebrates like insects and worms. As Lamarck worked through the museum's large collection of invertebrates, he was impressed by the number and variety of organisms . He became convinced that organisms could, in fact, change through time, stating that
... time and favorable conditions are the two principal means which nature has employed in giving existence to all her productions. We know that for her time has no limit, and that consequently she always has it at her disposal.
This was a radical departure from both the fixity concept and Cuvier's ideas, and it built on the long timescale that geologists had recently established. Lamarck proposed that changes that occurred during an organism 's lifetime could be passed on to their offspring, suggesting, for example, that a body builder's muscles would be inherited by their children.
As it turned out, the mechanism by which Lamarck proposed that organisms change over time was wrong, and he is now often referred to disparagingly for his "inheritance of acquired characteristics" idea. Yet despite the fact that some of his ideas were discredited, Lamarck established a support for evolutionary theory that others would build on and improve.
- Rock layers as evidence for evolution: Smith
In the early 1800s, a British geologist and canal surveyor named William Smith added another component to the accumulating evidence for evolution . Smith observed that rock layers exposed in different parts of England bore similarities to one another: These layers (or strata) were arranged in a predictable order, and each layer contained distinct groups of fossils . From this series of observations , he developed a hypothesis that specific groups of animals followed one another in a definite sequence through Earth's history, and this sequence could be seen in the rock layers. Smith's hypothesis was based on his knowledge of geological principles , including the Law of Superposition.
The Law of Superposition states that sediments are deposited in a time sequence, with the oldest sediments deposited first, or at the bottom, and newer layers deposited on top. The concept was first expressed by the Persian scientist Avicenna in the 11th century, but was popularized by the Danish scientist Nicolas Steno in the 17th century. Note that the law does not state how sediments are deposited; it simply describes the relationship between the ages of deposited sediments.
Figure 3: Engraving from William Smith's 1815 monograph on identifying strata by fossils.
Smith backed up his hypothesis with extensive drawings of fossils uncovered during his research (Figure 3), thus allowing other scientists to confirm or dispute his findings. His hypothesis has, in fact, been confirmed by many other scientists and has come to be referred to as the Law of Faunal Succession. His work was critical to the formation of evolutionary theory as it not only confirmed Cuvier's work that organisms have gone extinct , but it also showed that the appearance of life does not date to the birth of the planet. Instead, the fossil record preserves a timeline of the appearance and disappearance of different organisms in the past, and in doing so offers evidence for change in organisms over time.
- The theory of evolution by natural selection: Darwin and Wallace
It was into this world that Charles Darwin entered: Linnaeus had developed a taxonomy of organisms based on their physical relationships, Leclerc and Hutton demonstrated that there was sufficient time in Earth's history for organisms to change, Cuvier showed that species of organisms have gone extinct , Lamarck proposed that organisms change over time, and Smith established a timeline of the appearance and disappearance of different organisms in the geological record .
Figure 4: Title page of the 1859 Murray edition of the Origin of Species by Charles Darwin.
Charles Darwin collected data during his work as a naturalist on the HMS Beagle starting in 1831. He took extensive notes on the geology of the places he visited; he made a major find of fossils of extinct animals in Patagonia and identified an extinct giant ground sloth named Megatherium . He experienced an earthquake in Chile that stranded beds of living mussels above water, where they would be preserved for years to come.
Perhaps most famously, he conducted extensive studies of animals on the Galápagos Islands, noting subtle differences in species of mockingbird, tortoise, and finch that were isolated on different islands with different environmental conditions. These subtle differences made the animals highly adapted to their environments .
This broad spectrum of data led Darwin to propose an idea about how organisms change "by means of natural selection" (Figure 4). But this idea was not based only on his work, it was also based on the accumulation of evidence and ideas of many others before him. Because his proposal encompassed and explained many different lines of evidence and previous work, they formed the basis of a new and robust scientific theory regarding change in organisms – the theory of evolution by natural selection .
Darwin's ideas were grounded in evidence and data so compelling that if he had not conceived them, someone else would have. In fact, someone else did. Between 1858 and 1859, Alfred Russel Wallace , a British naturalist, wrote a series of letters to Darwin that independently proposed natural selection as the means for evolutionary change. The letters were presented to the Linnean Society of London, a prominent scientific society at the time (see our module on Scientific Institutions and Societies ). This long chain of research highlights that theories are not just the work of one individual. At the same time, however, it often takes the insight and creativity of individuals to put together all of the pieces and propose a new theory . Both Darwin and Wallace were experienced naturalists who were familiar with the work of others. While all of the work leading up to 1830 contributed to the theory of evolution , Darwin's and Wallace's theory changed the way that future research was focused by presenting a comprehensive, well-substantiated set of ideas, thus becoming a fundamental theory of biological research.
- Expanding, testing, and refining scientific theories
- Genetics and evolution: Mendel and Dobzhansky
Since Darwin and Wallace first published their ideas, extensive research has tested and expanded the theory of evolution by natural selection . Darwin had no concept of genes or DNA or the mechanism by which characteristics were inherited within a species . A contemporary of Darwin's, the Austrian monk Gregor Mendel , first presented his own landmark study, Experiments in Plant Hybridization, in 1865 in which he provided the basic patterns of genetic inheritance , describing which characteristics (and evolutionary changes) can be passed on in organisms (see our Genetics I module for more information). Still, it wasn't until much later that a "gene" was defined as the heritable unit.
In 1937, the Ukrainian born geneticist Theodosius Dobzhansky published Genetics and the Origin of Species , a seminal work in which he described genes themselves and demonstrated that it is through mutations in genes that change occurs. The work defined evolution as "a change in the frequency of an allele within a gene pool" ( Dobzhansky, 1982 ). These studies and others in the field of genetics have added to Darwin's work, expanding the scope of the theory .
- Evolution under a microscope: Lenski
More recently, Dr. Richard Lenski, a scientist at Michigan State University, isolated a single Escherichia coli bacterium in 1989 as the first step of the longest running experimental test of evolutionary theory to date – a true test meant to replicate evolution and natural selection in the lab.
After the single microbe had multiplied, Lenski isolated the offspring into 12 different strains , each in their own glucose-supplied culture, predicting that the genetic make-up of each strain would change over time to become more adapted to their specific culture as predicted by evolutionary theory . These 12 lines have been nurtured for over 40,000 bacterial generations (luckily bacterial generations are much shorter than human generations) and exposed to different selective pressures such as heat , cold, antibiotics, and infection with other microorganisms. Lenski and colleagues have studied dozens of aspects of evolutionary theory with these genetically isolated populations . In 1999, they published a paper that demonstrated that random genetic mutations were common within the populations and highly diverse across different individual bacteria . However, "pivotal" mutations that are associated with beneficial changes in the group are shared by all descendants in a population and are much rarer than random mutations, as predicted by the theory of evolution by natural selection (Papadopoulos et al., 1999).
- Punctuated equilibrium: Gould and Eldredge
While established scientific theories like evolution have a wealth of research and evidence supporting them, this does not mean that they cannot be refined as new information or new perspectives on existing data become available. For example, in 1972, biologist Stephen Jay Gould and paleontologist Niles Eldredge took a fresh look at the existing data regarding the timing by which evolutionary change takes place. Gould and Eldredge did not set out to challenge the theory of evolution; rather they used it as a guiding principle and asked more specific questions to add detail and nuance to the theory. This is true of all theories in science: they provide a framework for additional research. At the time, many biologists viewed evolution as occurring gradually, causing small incremental changes in organisms at a relatively steady rate. The idea is referred to as phyletic gradualism , and is rooted in the geological concept of uniformitarianism . After reexamining the available data, Gould and Eldredge came to a different explanation, suggesting that evolution consists of long periods of stability that are punctuated by occasional instances of dramatic change – a process they called punctuated equilibrium .
Like Darwin before them, their proposal is rooted in evidence and research on evolutionary change, and has been supported by multiple lines of evidence. In fact, punctuated equilibrium is now considered its own theory in evolutionary biology. Punctuated equilibrium is not as broad of a theory as natural selection . In science, some theories are broad and overarching of many concepts, such as the theory of evolution by natural selection; others focus on concepts at a smaller, or more targeted, scale such as punctuated equilibrium. And punctuated equilibrium does not challenge or weaken the concept of natural selection; rather, it represents a change in our understanding of the timing by which change occurs in organisms , and a theory within a theory. The theory of evolution by natural selection now includes both gradualism and punctuated equilibrium to describe the rate at which change proceeds.
- Hypotheses and laws: Other scientific concepts
One of the challenges in understanding scientific terms like theory is that there is not a precise definition even within the scientific community. Some scientists debate over whether certain proposals merit designation as a hypothesis or theory , and others mistakenly use the terms interchangeably. But there are differences in these terms. A hypothesis is a proposed explanation for an observable phenomenon. Hypotheses , just like theories , are based on observations from research . For example, LeClerc did not hypothesize that Earth had cooled from a molten ball of iron as a random guess; rather, he developed this hypothesis based on his observations of information from meteorites.
A scientist often proposes a hypothesis before research confirms it as a way of predicting the outcome of study to help better define the parameters of the research. LeClerc's hypothesis allowed him to use known parameters (the cooling rate of iron) to do additional work. A key component of a formal scientific hypothesis is that it is testable and falsifiable. For example, when Richard Lenski first isolated his 12 strains of bacteria , he likely hypothesized that random mutations would cause differences to appear within a period of time in the different strains of bacteria. But when a hypothesis is generated in science, a scientist will also make an alternative hypothesis , an explanation that explains a study if the data do not support the original hypothesis. If the different strains of bacteria in Lenski's work did not diverge over the indicated period of time, perhaps the rate of mutation was slower than first thought.
So you might ask, if theories are so well supported, do they eventually become laws? The answer is no – not because they aren't well-supported, but because theories and laws are two very different things. Laws describe phenomena, often mathematically. Theories, however, explain phenomena. For example, in 1687 Isaac Newton proposed a Theory of Gravitation, describing gravity as a force of attraction between two objects. As part of this theory, Newton developed a Law of Universal Gravitation that explains how this force operates. This law states that the force of gravity between two objects is inversely proportional to the square of the distance between those objects. Newton 's Law does not explain why this is true, but it describes how gravity functions (see our Gravity: Newtonian Relationships module for more detail). In 1916, Albert Einstein developed his theory of general relativity to explain the mechanism by which gravity has its effect. Einstein's work challenges Newton's theory, and has been found after extensive testing and research to more accurately describe the phenomenon of gravity. While Einstein's work has replaced Newton's as the dominant explanation of gravity in modern science, Newton's Law of Universal Gravitation is still used as it reasonably (and more simply) describes the force of gravity under many conditions. Similarly, the Law of Faunal Succession developed by William Smith does not explain why organisms follow each other in distinct, predictable ways in the rock layers, but it accurately describes the phenomenon.
Theories, hypotheses , and laws drive scientific progress
Theories, hypotheses , and laws are not simply important components of science, they drive scientific progress. For example, evolutionary biology now stands as a distinct field of science that focuses on the origins and descent of species . Geologists now rely on plate tectonics as a conceptual model and guiding theory when they are studying processes at work in Earth's crust . And physicists refer to atomic theory when they are predicting the existence of subatomic particles yet to be discovered. This does not mean that science is "finished," or that all of the important theories have been discovered already. Like evolution , progress in science happens both gradually and in short, dramatic bursts. Both types of progress are critical for creating a robust knowledge base with data as the foundation and scientific theories giving structure to that knowledge.
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- Theories, hypotheses, and laws drive scientific progress
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Hypothesis, Model, Theory, and Law
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- Physics Laws, Concepts, and Principles
- Quantum Physics
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- M.S., Mathematics Education, Indiana University
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In common usage, the words hypothesis, model, theory, and law have different interpretations and are at times used without precision, but in science they have very exact meanings.
Perhaps the most difficult and intriguing step is the development of a specific, testable hypothesis. A useful hypothesis enables predictions by applying deductive reasoning, often in the form of mathematical analysis. It is a limited statement regarding the cause and effect in a specific situation, which can be tested by experimentation and observation or by statistical analysis of the probabilities from the data obtained. The outcome of the test hypothesis should be currently unknown, so that the results can provide useful data regarding the validity of the hypothesis.
Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable. The concept of atoms was proposed by the ancient Greeks , who had no means of testing it. Centuries later, when more knowledge became available, the hypothesis gained support and was eventually accepted by the scientific community, though it has had to be amended many times over the year. Atoms are not indivisible, as the Greeks supposed.
A model is used for situations when it is known that the hypothesis has a limitation on its validity. The Bohr model of the atom , for example, depicts electrons circling the atomic nucleus in a fashion similar to planets in the solar system. This model is useful in determining the energies of the quantum states of the electron in the simple hydrogen atom, but it is by no means represents the true nature of the atom. Scientists (and science students) often use such idealized models to get an initial grasp on analyzing complex situations.
Theory and Law
A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a theory is an explanation for a set of related phenomena, like the theory of evolution or the big bang theory .
The word "law" is often invoked in reference to a specific mathematical equation that relates the different elements within a theory. Pascal's Law refers an equation that describes differences in pressure based on height. In the overall theory of universal gravitation developed by Sir Isaac Newton , the key equation that describes the gravitational attraction between two objects is called the law of gravity .
These days, physicists rarely apply the word "law" to their ideas. In part, this is because so many of the previous "laws of nature" were found to be not so much laws as guidelines, that work well within certain parameters but not within others.
Scientific Paradigms
Once a scientific theory is established, it is very hard to get the scientific community to discard it. In physics, the concept of ether as a medium for light wave transmission ran into serious opposition in the late 1800s, but it was not disregarded until the early 1900s, when Albert Einstein proposed alternate explanations for the wave nature of light that did not rely upon a medium for transmission.
The science philosopher Thomas Kuhn developed the term scientific paradigm to explain the working set of theories under which science operates. He did extensive work on the scientific revolutions that take place when one paradigm is overturned in favor of a new set of theories. His work suggests that the very nature of science changes when these paradigms are significantly different. The nature of physics prior to relativity and quantum mechanics is fundamentally different from that after their discovery, just as biology prior to Darwin’s Theory of Evolution is fundamentally different from the biology that followed it. The very nature of the inquiry changes.
One consequence of the scientific method is to try to maintain consistency in the inquiry when these revolutions occur and to avoid attempts to overthrow existing paradigms on ideological grounds.
Occam’s Razor
One principle of note in regards to the scientific method is Occam’s Razor (alternately spelled Ockham's Razor), which is named after the 14th century English logician and Franciscan friar William of Ockham. Occam did not create the concept—the work of Thomas Aquinas and even Aristotle referred to some form of it. The name was first attributed to him (to our knowledge) in the 1800s, indicating that he must have espoused the philosophy enough that his name became associated with it.
The Razor is often stated in Latin as:
entia non sunt multiplicanda praeter necessitatem
or, translated to English:
entities should not be multiplied beyond necessity
Occam's Razor indicates that the most simple explanation that fits the available data is the one which is preferable. Assuming that two hypotheses presented have equal predictive power, the one which makes the fewest assumptions and hypothetical entities takes precedence. This appeal to simplicity has been adopted by most of science, and is invoked in this popular quote by Albert Einstein:
Everything should be made as simple as possible, but not simpler.
It is significant to note that Occam's Razor does not prove that the simpler hypothesis is, indeed, the true explanation of how nature behaves. Scientific principles should be as simple as possible, but that's no proof that nature itself is simple.
However, it is generally the case that when a more complex system is at work there is some element of the evidence which doesn't fit the simpler hypothesis, so Occam's Razor is rarely wrong as it deals only with hypotheses of purely equal predictive power. The predictive power is more important than the simplicity.
Edited by Anne Marie Helmenstine, Ph.D.
- The Basics of Physics in Scientific Study
- Kinetic Molecular Theory of Gases
- De Broglie Hypothesis
- An Introduction to Brownian Motion
- The History of Gravity
- History of the Michelson-Morley Experiment
- Newton's Law of Gravity
- Wave Particle Duality and How It Works
- What Is the Boltzmann Brains Hypothesis?
- Five Great Problems in Theoretical Physics
- The Basics of String Theory
- Understanding Cosmology and Its Impact
- An Idealized Model in Physics
- Albert Einstein: What Is Unified Field Theory?
- What Is the Steady-State Theory in Cosmology?
- What Is Model-Dependent Realism?
- Comment Rules
- Global Warming
- Nature of Science
- Vaccines/Alt. Medicines
Facts, Hypotheses, Theories, and Laws: What’s the Difference?
Perhaps no topic in science garners more confusion among the general public than the distinction between a theory and a hypothesis. This confusion is highly regrettable, because the distinction is one of the most fundamental concepts in science, and a lack of understanding about these definitions leads to a great deal of confusion. Therefore, I will attempt to alleviate the maelstrom of nonsense and bewilderment surrounding these terms and endow my readers with a proper understanding of their meanings.
Let’s begin with the definition of “fact.” This is actually the hardest of these terms to define. Basically, it’s just something that has been observed and tested and shown to be true. Importantly, facts generally don’t offer explanations, they are just how things are. If we want an explanation of why things are the way that they are, we have to turn to hypotheses and theories.
This is where most people mess up. In the common vernacular, a theory is “an educated guess,” but in science, an educated guess is a hypothesis, not a theory. Further, when I ask my students to define a theory, I often get answers like, “something that we think is true, but haven’t tested,” or even worse, “an idea that can’t be tested.” Television further reinforces these misconceptions, by constantly misusing “theory.” In virtually every episode of shows like “House M.D.” and “Bones” someone says, “my theory is that…” The reality is that in science, a theory is much, much more than just an educated guess. In fact, theories are the highest form of scientific certainty. They have been rigorously test over and over again and they have been shown to have a very high predictive power. In other words, they consistently and accurately predict the outcomes of experiments.
For example, suppose that I am currently holding a pen in the air. What will happen if I release my hand? Hopefully, you all thought, “the pen will drop,” but why did you make that prediction? In fact, you were simply applying the theory of universal gravity. This is the theory that all bodies produce gravity and are acted upon by the gravity of other bodies. Also note that by dropping the pen, I would demonstrate the fact of gravity. In other words, it is a fact that gravity took hold of the pen and caused it to fall. To explain that fact, we apply the theory of universal gravity which tells us that the earth produces a field of gravity which attracted the pen (in reality of course the theory also tells us the exact rate of acceleration of the pen). So you see, we use theories to explain facts. As such, they actually supersede facts in their certainty and importance.
So if a theory is an explanatory framework with a high predictive power, what then is a hypothesis? A hypothesis is basically an educated guess. It’s a possible explanation that hasn’t yet achieved the certainty of a theory. There may be experimental support behind it, but not on the level that a theory has. It is, however, entirely possible for a hypothesis to become a theory once enough evidence has been accumulated.
At this point, you all are probably wondering what a law is, because my explanation of a theory probably sounds a lot like what you expected for the definition of a law, and there is a very good reason for that. Namely, the terms “theory” and “law” are essentially synonymous. “Law” is an older term that we don’t use as much anymore, but it has the same level of certainty as a theory. For example, the law of universal gravity and the theory of universal gravity are synonyms. They mean the exact same thing and either one is equally correct.
So why does this matter? Other than scientists, who really cares if people say “theory” when they mean “hypothesis?” The reality is that this confusion leads to a great many misunderstandings and faulty arguments. The most prominent example is the argument that, “evolution shouldn’t be being taught as a fact because it’s just a theory.” As we’ve just seen, theories are actually our highest form of scientific certainty, and they actually supersede facts because they explain the facts. So saying, “evolution is just a theory” is no different from saying, “gravity is just a law.” Theories make up the cornerstones of every branch of science. For example, the germ theory of disease states that viruses, bacteria, etc. make us sick, cell theory states that all living things are made of cells, atomic theory states that all matter is made of atoms, etc. Obviously, there aren’t any outcries about people teaching the notion that matter is made of elements as a fact, even though its “just a theory.” Further, all theories contain a factual component because they explain the facts (I illustrated this previously with my gravity example). So, when it comes to evolution, the idea that life on this planet has slowly changed over millions of years is considered scientific fact. We have ample evidence for it from fossils, genetics, etc. The theory is the “theory of evolution by natural selection” which states that natural selection has been the primary driver of evolution. So the core thing that most creationists oppose (i.e., the idea that life has evolved) is not a theory, it is a fact. The theory of natural selection simply explains what caused those changes to take place.
In summary, a fact is a tested and confirmed observation or measurement. A hypothesis is basically an educated guess, and the terms theory and law synonymously describe a thoroughly tested explanatory framework which has a high predictive power and explains facts.
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Science Connected Magazine
Science Literacy, Education, Communication
Theory vs. Hypothesis vs. Law… Explained!
Some people try to attack things like evolution by natural selection and man-made climate change by saying “Oh, that’s just a THEORY!”
Yes, they are both theories. Stop saying it like it’s a bad thing! It’s time to learn the difference between a fact, a theory, a hypothesis, and a scientific law.
Special thanks to Joe Hanson, Ph.D., for allowing us to publish his terrific videos.
It’s Okay To Be Smart is written and hosted by Joe Hanson, Ph.D. @jtotheizzoe Facebook: http://www.facebook.com/itsokaytobesmart For more awesome science, check out: http://www.itsokaytobesmart.com Produced by PBS Digital Studios: http://www.youtube.com/user/pbsdigita…
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The Scientific Hypothesis
The Key to Understanding How Science Works
Hypotheses, Theories, Laws (and Models)… What’s the difference?
Untold hours have been spent trying to sort out the differences between these ideas. should we bother.
Ask what the differences between these concepts are and you’re likely to encounter a raft of distinctions; typically with charts and ladders of generality leading from hypotheses to theories and, ultimately, to laws. Countless students have been exposed to and forced to learn how the schemes are set up. Theories are said to be well-tested hypotheses, or maybe whole collections of linked hypotheses, and laws, well, laws are at the top of the heap, the apex of science having enormous reach, quantitative predictive power, and validity. It all seems so clear.
Yet there are many problems with the general scheme. For one thing, it is never quite explained how a hypothesis turns into a theory or law and, consequently, the boundaries are blurry, and definitions tend vary with the speaker. And there is no consistency in usage across fields, I’ll give some examples in a minute. There are branches of science that have few if any theories and no laws – neuroscience comes to mind – though no one doubts that neuroscience is a bona fide science that has discovered great quantities of reliable and useful information and wide-ranging generalizations. At the other extreme, there are sciences that spin out theories at a dizzying pace – psychology, for instance – although the permanence and indeed the veracity of psychological theories are rarely on par with those of physics or chemistry.
Some people will tell you that theories and laws are “more quantitative” than hypotheses, but the most famous theory in biology, the Theory of Evolution, which is based on concepts such as heritability, genetic variability, natural selection, etc. is not as neatly expressible in quantitative terms as is Newton’s Theory of Gravity, for example. And what do we make of the fact that Newton’s “Law of Gravity” was superceded by Einstein’s “General Theory (not Law) of Relativity?”
What about the idea that a hypothesis is a low-level explanation that somehow transmogrifies into a theory when conditions are right? Even this simple rule is not adhered to. Take geology (or “geoscience” nowadays): We have the Alvarez Hypothesis about how an asteroid slamming into the earth caused the extinction of dinosaurs and other life-forms ~66 million years ago. The Alvarez Hypothesis explains, often in quantitative detail, many important phenomena and makes far-reaching predictions, most remarkably of a crater, which was eventually found in the Yucatan peninsula, that has the right age and size to be the site of an extinction-causing asteroid impact. The Alvarez Hypothesis has been rigorously tested many times since it was proposed, without having been promoted to a theory.
But perhaps the Alvarez Hypothesis is still thought to be a tentative explanation, not yet worthy of a more exalted status? It seems that the same can’t be said about the idea that the earth’s crust consists of 12 or so rigid “plates” of solid material that drift around very slowly and create geological phenomena, such as mountain ranges and earth-quakes, when they crash into each other. This is called either the “Plate Tectonics Hypothesis” or “Plate Tectonics Theory” by different authors. Same data, same interpretations, same significance, different names.
And for anyone trying to make sense of the hypothesis-theory-law progression, it must be highly confusing to learn that the crowning achievement of modern physics – itself the “queen of the sciences” – is a complex, extraordinarily precise, quantitative structure is known as the Standard Model of Particle Physics, not the Standard Theory, or the Standard Law! The Standard Model incorporates three of the four major forces of nature, describes many subatomic particles, and has successfully predicted numerous subtle properties of subatomic particles. Does this mean that “model” now implies a large, well-worked out and self-consistent body of scientific knowledge? Not at all; in fact, “model” and “hypothesis” are used interchangeably at the simplest levels of experimental investigation in biology, neuroscience, etc., so definition-wise, we’re back to the beginning.
The reason that the Standard Model is a model and not a theory seems basically to be the same as the reason that the Alvarez Hypothesis is a hypothesis and not a theory or that Evolution is a theory and not a law: essentially it is a matter of convention, tradition, or convenience. The designations, we can infer, are primarily names that lack exact substantive, generally agreed-on definitions.
So, rather than worrying about any profound distinctions between hypotheses, theories, laws (and models) it might be more helpful to look at the properties that they have in common:
1. They are all “conjectural” which, for the moment, means that they are inventions of the human mind.
2. They make specific predictions that are empirically testable, in principle.
3. They are falsifiable – if their predictions are false, they are false – though not provable, by experiment or observation.
4. As a consequence of point 3., hypotheses, theories, and laws are all provisional; they may be replaced as further information becomes available.
“Hypothesis,” it seems to me, is the fundamental unit, the building block, of scientific thinking. It is the term that is most consistently used by all sciences; it is more basic than any theory; it carries the least baggage, is the least susceptible to multiple interpretations and, accordingly, is the most likely to communicate effectively. These advantages are relative of course; as I’ll get into elsewhere, even “hypothesis” is the subject of misinterpretation. In any case, its simplicity and clarity are why this website is devoted to the Scientific Hypothesis and not the others.
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Hypotheses, Theories and Laws
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Although we tend to speak of hypotheses, theories, and laws as though they were clearly differentiated, this is not the case; the distinctions are not clear and are primarily a matter of belief regarding how well relationships that have been conjectured are supported by evidence. But scientific theories and laws are far more than just matters of faith; they are also the product of a methodology that has developed via continual confrontation with reality. It is not an exaggeration to state that scientific theories and laws are the most reliable forms of generalization produced by rational human activity. Faith and rationality can co-exist in science in a most vital symbiosis!
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We will see later on when the focus is on the test of hypotheses that this is the so-called “alternative hypothesis”, the hypothesis we are interested in and that motivates the study. The “null hypothesis” here would be that the behaviour of the dogs and monkeys in the ashram is not different from dogs and monkeys who do not frequent the ashram.
It should be noted here that Einstein did not just formulate his theory (which, in fact was a hypothesis that later became accepted as a theory) on the basis of intuition; his formulation of relativity theory was preceded by the Michelson-Morley experiment on the velocity of light.
The term “model”, which we have met several times until now, is often used interchangeably with “theory”, although it most often refers to a representation of a theory. In the case of many of the natural sciences, this representation is most often in the form of a mathematical model, i.e. a system of equations representing the interrelationships between variables. The term “model” often refers as well to physical or pictorial representations. Examples could be a physical structure representing a geocentric model of the universe or a visual model created on a computer (and generated by a mathematical model) of the double helix of DNA with its two polynucleotide strands woven around each other and running in opposite directions.
Having just considered an example involving fossils, I am tempted to mention that what is considered by many to be one of, if not the most successful and fundamental theories in the biosciences, that of evolution, is regarded by a number of leading scientists as a research programme rather than a theory. Aside from some of the programme’s underlying partial theories (dealing with such matters as macro- and microevolution and the molecular and genetic basis for the form and function of organisms), it has not been formalized, and there exist significant controversies as to its content and form (e.g. as to whether the development of new organisms has been more or less continuous or whether revolutionary changes such as the sudden development of completely different organisms have occurred)—as well as to whether the programme’s representations of organisms’ abilities to adapt, compete, cooperate and survive in fact represent a teleological perspective on the development of organisms. See e.g. (Depew and Weber 1996) and (Ward and Brownlee 2004).
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Pruzan, P. (2016). Hypotheses, Theories and Laws. In: Research Methodology. Springer, Cham. https://doi.org/10.1007/978-3-319-27167-5_3
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The Scientific Meaning of the Terms
Lay people often misinterpret the language used by scientists. And for that reason, they sometimes draw the wrong conclusions as to what the scientific terms mean.
Three such terms that are often used interchangeably are “scientific law,” “hypothesis,” and “theory.”
In layman’s terms, if something is said to be “just a theory,” it usually means that it is a mere guess, or is unproved. It might even lack credibility. But in scientific terms, a theory implies that something has been proven and is generally accepted as being true.
Here is what each of these terms means to a scientist:
This is a statement of fact meant to describe, in concise terms, an action or set of actions. It is generally accepted to be true and universal, and can sometimes be expressed in terms of a single mathematical equation. Scientific laws are similar to mathematical postulates. They don’t really need any complex external proofs; they are accepted at face value based upon the fact that they have always been observed to be true.
Specifically, scientific laws must be simple, true, universal, and absolute. They represent the cornerstone of scientific discovery, because if a law ever did not apply, then all science based upon that law would collapse.
Some scientific laws, or laws of nature, include the law of gravity, Newton’s laws of motion, the laws of thermodynamics, Boyle’s law of gases, the law of conservation of mass and energy, and Hook’s law of elasticity.
Hypothesis:
This is an educated guess based upon observation. It is a rational explanation of a single event or phenomenon based upon what is observed, but which has not been proved. Most hypotheses can be supported or refuted by experimentation or continued observation.
Scientific Theory:
A theory is what one or more hypotheses become once they have been verified and accepted to be true. A theory is an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. Unfortunately, even some scientists often use the term “theory” in a more colloquial sense, when they really mean to say “hypothesis.” That makes its true meaning in science even more confusing to the general public.
In general, both a scientific theory and a scientific law are accepted to be true by the scientific community as a whole. Both are used to make predictions of events. Both are used to advance technology.
In fact, some laws, such as the law of gravity, can also be theories when taken more generally. The law of gravity is expressed as a single mathematical expression and is presumed to be true all over the universe and all through time. Without such an assumption, we can do no science based on gravity’s effects. But from the law, we derived the theory of gravity which describes how gravity works, what causes it, and how it behaves. We also use that to develop another theory, Einstein’s General Theory of Relativity, in which gravity plays a crucial role. The basic law is intact, but the theory expands it to include various and complex situations involving space and time.
The biggest difference between a law and a theory is that a theory is much more complex and dynamic. A law describes a single action, whereas a theory explains an entire group of related phenomena. And, whereas a law is a postulate that forms the foundation of the scientific method, a theory is the end result of that same process.
A simple analogy can be made using a slingshot and an automobile.
A scientific law is like a slingshot. A slingshot has but one moving part–the rubber band. If you put a rock in it and draw it back, the rock will fly out at a predictable speed, depending upon the distance the band is drawn back.
An automobile has many moving parts, all working in unison to perform the chore of transporting someone from one point to another point. An automobile is a complex piece of machinery. Sometimes, improvements are made to one or more component parts. A new set of spark plugs that are composed of a better alloy that can withstand heat better, for example, might replace the existing set. But the function of the automobile as a whole remains unchanged.
A theory is like the automobile. Components of it can be changed or improved upon, without changing the overall truth of the theory as a whole.
Some scientific theories include the theory of evolution, the theory of relativity, the atomic theory, and the quantum theory. All of these theories are well documented and proved beyond reasonable doubt. Yet scientists continue to tinker with the component hypotheses of each theory in an attempt to make them more elegant and concise, or to make them more all-encompassing. Theories can be tweaked, but they are seldom, if ever, entirely replaced.
A theory is developed only through the scientific method, meaning it is the final result of a series of rigorous processes. Note that theories do not become laws. Scientific laws must exist prior to the start of using the scientific method because, as stated earlier, laws are the foundation for all science. Here is an oversimplified example of the development of a scientific theory:
Development of a Simple Theory by the Scientific Method:
- Start with an observation that evokes a question: Broth spoils when I leave it out for a couple of days. Why?
- Using logic and previous knowledge, state a possible answer, called a Hypothesis: Tiny organisms floating in the air must fall into the broth and start reproducing.
- Perform an experiment or Test: After boiling some broth, I divide it into two containers, one covered and one not covered. I place them on the table for two days and see if one spoils. Only the uncovered broth spoiled.
- Then publish your findings in a peer-reviewed journal. Publication: “Only broth that is exposed to the air after two days tended to spoil. The covered specimen did not.”
- Other scientists read about your experiment and try to duplicate it. Verification: Every scientist who tries your experiment comes up with the same results. So they try other methods to make sure your experiment was measuring what it was supposed to. Again, they get the same results every time.
- In time, and if experiments continue to support your hypothesis, it becomes a Scientific Theory: Microorganisms from the air cause broth to spoil.
Useful Prediction:
If I leave food items open to the air, they will spoil. If I want to keep them from spoiling, I will keep them covered.
Note, however, that although the prediction is useful, the theory does not absolutely prove that the next open container of broth will spoil. Thus it is said to be falsifiable. If anyone ever left a cup of broth open for days and it did not spoil, the theory would have to be tweaked or thrown out.
A real theory must be falsifiable. They must be capable of being modified based on new evidence. So-called “theories” based on religion, such as creationism or intelligent design are, therefore, not scientific theories. They are not falsifiable, they don’t depend on new evidence, and they do not follow the scientific method.
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Similarities and Differences Between Hypothesis and Theory
In the realm of scientific inquiry, two terms that are often used interchangeably but hold distinct meanings are “hypothesis” and “theory.” Both play crucial roles in the scientific method, contributing to the understanding and advancement of knowledge. This article delves into the similarities and differences between these two fundamental scientific concepts.
Hypothesis: The Starting Point
A hypothesis is a proposed explanation for a phenomenon. It is an educated guess or a tentative solution to a problem based on existing knowledge. Scientists formulate hypotheses to guide their research and make predictions that can be tested through experimentation or observation.
Characteristics
- Testability: A good hypothesis is testable, meaning it can be investigated through empirical methods.
- Falsifiability: It should be possible to prove the hypothesis false through experimentation or observation.
- Specificity: The hypothesis must be clear and specific, outlining the expected outcome of the experiment.
If plants receive more sunlight, then their growth rate will increase.
Theory: A Comprehensive Explanation
On the other hand, a theory is a well-substantiated explanation of some aspect of the natural world. Unlike a hypothesis, a theory has withstood extensive testing and scrutiny, providing a comprehensive framework for understanding a particular phenomenon.
- Explanatory Power: Theories explain a wide range of phenomena and observations.
- Predictive Capability: They can predict future observations and experiments accurately.
- Consistency: The components of a theory are internally consistent and align with existing scientific knowledge.
The theory of evolution explains the biodiversity of life through the processes of natural selection and genetic variation.
Similarities
1. both guide scientific inquiry.
Both hypotheses and theories play integral roles in the scientific method, guiding researchers in the pursuit of knowledge. Hypotheses set the initial direction for experiments, while theories provide overarching frameworks.
2. Subject to Revision
Scientific knowledge is dynamic, and both hypotheses and theories are subject to revision based on new evidence. As more data becomes available, scientists may refine or even discard hypotheses and theories.
Differences
1. level of certainty.
The primary distinction lies in the level of certainty associated with each term. A hypothesis is a tentative explanation that requires testing, while a theory is a well-established explanation supported by a substantial body of evidence.
Hypotheses are narrow in scope, addressing specific questions or problems, while theories have a broader scope, encompassing a wide range of related phenomena.
In conclusion, hypotheses and theories are essential components of the scientific process, each serving distinct roles. Hypotheses initiate investigations, while theories provide robust explanations for observed phenomena. Recognizing the differences and similarities between these concepts is crucial for understanding how scientific knowledge evolves and progresses.
Related References:
- Scientific Method – Wikipedia
- Understanding Science – University of California Museum of Paleontology
- The Difference Between Hypothesis and Theory – ThoughtCo
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Hypothesis vs. Theory
A hypothesis is either a suggested explanation for an observable phenomenon, or a reasoned prediction of a possible causal correlation among multiple phenomena. In science , a theory is a tested, well-substantiated, unifying explanation for a set of verified, proven factors. A theory is always backed by evidence; a hypothesis is only a suggested possible outcome, and is testable and falsifiable.
Comparison chart
Examples of theory and hypothesis.
Theory: Einstein's theory of relativity is a theory because it has been tested and verified innumerable times, with results consistently verifying Einstein's conclusion. However, simply because Einstein's conclusion has become a theory does not mean testing of this theory has stopped; all science is ongoing. See also the Big Bang theory , germ theory , and climate change .
Hypothesis: One might think that a prisoner who learns a work skill while in prison will be less likely to commit a crime when released. This is a hypothesis, an "educated guess." The scientific method can be used to test this hypothesis, to either prove it is false or prove that it warrants further study. (Note: Simply because a hypothesis is not found to be false does not mean it is true all or even most of the time. If it is consistently true after considerable time and research, it may be on its way to becoming a theory.)
This video further explains the difference between a theory and a hypothesis:
Common Misconception
People often tend to say "theory" when what they're actually talking about is a hypothesis. For instance, "Migraines are caused by drinking coffee after 2 p.m. — well, it's just a theory, not a rule."
This is actually a logically reasoned proposal based on an observation — say 2 instances of drinking coffee after 2 p.m. caused a migraine — but even if this were true, the migraine could have actually been caused by some other factors.
Because this observation is merely a reasoned possibility, it is testable and can be falsified — which makes it a hypothesis, not a theory.
- What is a Scientific Hypothesis? - LiveScience
- Wikipedia:Scientific theory
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Comments: Hypothesis vs Theory
Anonymous comments (2).
October 11, 2013, 1:11pm "In science, a theory is a well-substantiated, unifying explanation for a set of verified, proven hypotheses." But there's no such thing as "proven hypotheses". Hypotheses can be tested/falsified, they can't be "proven". That's just not how science works. Logical deductions based on axioms can be proven, but not scientific hypotheses. On top of that I find it somewhat strange to claim that a theory doesn't have to be testable, if it's built up from hypotheses, which DO have to be testable... — 80.✗.✗.139
May 6, 2014, 11:45pm "Evolution is a theory, not a fact, regarding the origin of living things." this statement is poorly formed because it implies that a thing is a theory until it gets proven and then it is somehow promoted to fact. this is just a misunderstanding of what the words mean, and of how science progresses generally. to say that a theory is inherently dubious because "it isn't a fact" is pretty much a meaningless statement. no expression which qualified as a mere fact could do a very good job of explaining the complicated process by which species have arisen on Earth over the last billion years. in fact, if you claimed that you could come up with such a single fact, now THAT would be dubious! everything we observe in nature supports the theory of evolution, and nothing we observe contradicts it. when you can say this about a theory, it's a pretty fair bet that the theory is correct. — 71.✗.✗.151
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This is the Difference Between a Hypothesis and a Theory
What to Know A hypothesis is an assumption made before any research has been done. It is formed so that it can be tested to see if it might be true. A theory is a principle formed to explain the things already shown in data. Because of the rigors of experiment and control, it is much more likely that a theory will be true than a hypothesis.
As anyone who has worked in a laboratory or out in the field can tell you, science is about process: that of observing, making inferences about those observations, and then performing tests to see if the truth value of those inferences holds up. The scientific method is designed to be a rigorous procedure for acquiring knowledge about the world around us.
In scientific reasoning, a hypothesis is constructed before any applicable research has been done. A theory, on the other hand, is supported by evidence: it's a principle formed as an attempt to explain things that have already been substantiated by data.
Toward that end, science employs a particular vocabulary for describing how ideas are proposed, tested, and supported or disproven. And that's where we see the difference between a hypothesis and a theory .
A hypothesis is an assumption, something proposed for the sake of argument so that it can be tested to see if it might be true.
In the scientific method, the hypothesis is constructed before any applicable research has been done, apart from a basic background review. You ask a question, read up on what has been studied before, and then form a hypothesis.
What is a Hypothesis?
A hypothesis is usually tentative, an assumption or suggestion made strictly for the objective of being tested.
When a character which has been lost in a breed, reappears after a great number of generations, the most probable hypothesis is, not that the offspring suddenly takes after an ancestor some hundred generations distant, but that in each successive generation there has been a tendency to reproduce the character in question, which at last, under unknown favourable conditions, gains an ascendancy. Charles Darwin, On the Origin of Species , 1859 According to one widely reported hypothesis , cell-phone transmissions were disrupting the bees' navigational abilities. (Few experts took the cell-phone conjecture seriously; as one scientist said to me, "If that were the case, Dave Hackenberg's hives would have been dead a long time ago.") Elizabeth Kolbert, The New Yorker , 6 Aug. 2007
What is a Theory?
A theory , in contrast, is a principle that has been formed as an attempt to explain things that have already been substantiated by data. It is used in the names of a number of principles accepted in the scientific community, such as the Big Bang Theory . Because of the rigors of experimentation and control, its likelihood as truth is much higher than that of a hypothesis.
It is evident, on our theory , that coasts merely fringed by reefs cannot have subsided to any perceptible amount; and therefore they must, since the growth of their corals, either have remained stationary or have been upheaved. Now, it is remarkable how generally it can be shown, by the presence of upraised organic remains, that the fringed islands have been elevated: and so far, this is indirect evidence in favour of our theory . Charles Darwin, The Voyage of the Beagle , 1839 An example of a fundamental principle in physics, first proposed by Galileo in 1632 and extended by Einstein in 1905, is the following: All observers traveling at constant velocity relative to one another, should witness identical laws of nature. From this principle, Einstein derived his theory of special relativity. Alan Lightman, Harper's , December 2011
Non-Scientific Use
In non-scientific use, however, hypothesis and theory are often used interchangeably to mean simply an idea, speculation, or hunch (though theory is more common in this regard):
The theory of the teacher with all these immigrant kids was that if you spoke English loudly enough they would eventually understand. E. L. Doctorow, Loon Lake , 1979 Chicago is famous for asking questions for which there can be no boilerplate answers. Example: given the probability that the federal tax code, nondairy creamer, Dennis Rodman and the art of mime all came from outer space, name something else that has extraterrestrial origins and defend your hypothesis . John McCormick, Newsweek , 5 Apr. 1999 In his mind's eye, Miller saw his case suddenly taking form: Richard Bailey had Helen Brach killed because she was threatening to sue him over the horses she had purchased. It was, he realized, only a theory , but it was one he felt certain he could, in time, prove. Full of urgency, a man with a mission now that he had a hypothesis to guide him, he issued new orders to his troops: Find out everything you can about Richard Bailey and his crowd. Howard Blum, Vanity Fair , January 1995
And sometimes one term is used as a genus, or a means for defining the other:
Laplace's popular version of his astronomy, the Système du monde , was famous for introducing what came to be known as the nebular hypothesis , the theory that the solar system was formed by the condensation, through gradual cooling, of the gaseous atmosphere (the nebulae) surrounding the sun. Louis Menand, The Metaphysical Club , 2001 Researchers use this information to support the gateway drug theory — the hypothesis that using one intoxicating substance leads to future use of another. Jordy Byrd, The Pacific Northwest Inlander , 6 May 2015 Fox, the business and economics columnist for Time magazine, tells the story of the professors who enabled those abuses under the banner of the financial theory known as the efficient market hypothesis . Paul Krugman, The New York Times Book Review , 9 Aug. 2009
Incorrect Interpretations of "Theory"
Since this casual use does away with the distinctions upheld by the scientific community, hypothesis and theory are prone to being wrongly interpreted even when they are encountered in scientific contexts—or at least, contexts that allude to scientific study without making the critical distinction that scientists employ when weighing hypotheses and theories.
The most common occurrence is when theory is interpreted—and sometimes even gleefully seized upon—to mean something having less truth value than other scientific principles. (The word law applies to principles so firmly established that they are almost never questioned, such as the law of gravity.)
This mistake is one of projection: since we use theory in general use to mean something lightly speculated, then it's implied that scientists must be talking about the same level of uncertainty when they use theory to refer to their well-tested and reasoned principles.
The distinction has come to the forefront particularly on occasions when the content of science curricula in schools has been challenged—notably, when a school board in Georgia put stickers on textbooks stating that evolution was "a theory, not a fact, regarding the origin of living things." As Kenneth R. Miller, a cell biologist at Brown University, has said , a theory "doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”
While theories are never completely infallible, they form the basis of scientific reasoning because, as Miller said "to the best of our ability, we’ve tested them, and they’ve held up."
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A hypothesis is an educated guess, based on observation. It's a prediction of cause and effect. Usually, a hypothesis can be supported or refuted through experimentation or more observation. A hypothesis can be disproven but not proven to be true. Example: If you see no difference in the cleaning ability of various laundry detergents, you might ...
A hypothesis is a possible explanation that can be tested. This simple definition needs some further explanation. It says it must have a possible explanation. The hypothesis should apply reasoning ...
The words "fact," "hypothesis," "theory," and "law" have very specific meanings in the world of science, and they don't exactly match the ones we use in everyday language. 1130913708. professor writing on the board while having a chalk and blackboard lecture (shallow DOF; color toned image)
Definitions. A (causal) hypothesis is a proposed explanation. A prediction is the expected result of a test that is derived, by deduction, from a hypothesis or theory. A law (or rule or principle) is a statement that summarises an observed regularity or pattern in nature.
Some scientists debate over whether certain proposals merit designation as a hypothesis or theory, and others mistakenly use the terms interchangeably. But there are differences in these terms. A hypothesis is a proposed explanation for an observable phenomenon. Hypotheses, just like theories, are based on observations from research. For ...
Theory and Law. A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a theory is an explanation for a set of related phenomena, like the theory of evolution or the big bang theory.
Hypothesis: the core of the scientific method. The scientific method is an empirical procedure that consists of systematic observation, measurement, and experiment, and the formulation, testing ...
In summary, a fact is a tested and confirmed observation or measurement. A hypothesis is basically an educated guess, and the terms theory and law synonymously describe a thoroughly tested explanatory framework which has a high predictive power and explains facts.
Yes, they are both theories. Stop saying it like it's a bad thing! It's time to learn the difference between a fact, a theory, a hypothesis, and a scientific law. Special thanks to Joe Hanson, Ph.D., for allowing us to publish his terrific videos. It's Okay To Be Smart is written and hosted by Joe Hanson, Ph.D. @jtotheizzoe.
Theory vs. Law: Basics of the Scientific Method. The scientific method involves formulating hypotheses and testing them to see if they hold up to the realities of the natural world. Successfully proven hypotheses can lead to either scientific theories or scientific laws, which are similar in character but are not synonymous terms.
2. They make specific predictions that are empirically testable, in principle. 3. They are falsifiable - if their predictions are false, they are false - though not provable, by experiment or observation. 4. As a consequence of point 3., hypotheses, theories, and laws are all provisional; they may be replaced as further information becomes ...
Abstract. Although we tend to speak of hypotheses, theories, and laws as though they were clearly differentiated, this is not the case; the distinctions are not clear and are primarily a matter of belief regarding how well relationships that have been conjectured are supported by evidence. But scientific theories and laws are far more than just ...
Though closely related, scientific law vs. theory are two different terms. Learn about their key differences in science with this helpful article. Dictionary ... the hypothesis can become a theory. atomic theory - Atomic theory indicates that all matter is made up of atoms, which are microscopic particles that cannot be divided, created or ...
A law describes a single action, whereas a theory explains an entire group of related phenomena. And, whereas a law is a postulate that forms the foundation of the scientific method, a theory is the end result of that same process. A simple analogy can be made using a slingshot and an automobile. A scientific law is like a slingshot.
A hypothesis is a tentative explanation that requires testing, while a theory is a well-established explanation supported by a substantial body of evidence. 2. Scope. Hypotheses are narrow in scope, addressing specific questions or problems, while theories have a broader scope, encompassing a wide range of related phenomena.
A hypothesis is either a suggested explanation for an observable phenomenon, or a reasoned prediction of a possible causal correlation among multiple phenomena. In science, a theory is a tested, well-substantiated, unifying explanation for a set of verified, proven factors. A theory is always backed by evidence; a hypothesis is only a suggested possible outcome, and is testable and falsifiable.
Fact: Observations about the world around us. Example: "It's bright outside.". Hypothesis: A proposed explanation for a phenomenon made as a starting point for further investigation. Example ...
A hypothesis is an assumption made before any research has been done. It is formed so that it can be tested to see if it might be true. A theory is a principle formed to explain the things already shown in data. Because of the rigors of experiment and control, it is much more likely that a theory will be true than a hypothesis.