define the terms fact hypothesis theory and law

• 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.

Share this:

• Search for:

Follow The Logic of Science on Facebook.

Follow The Logic of Science via Email

Enter your email address to follow this blog and receive notifications of new posts by email.

Email Address:

• May 2024  (1)
• April 2024  (1)
• January 2024  (1)
• September 2022  (1)
• July 2022  (1)
• January 2022  (2)
• August 2021  (1)
• July 2021  (1)
• June 2021  (2)
• March 2021  (1)
• October 2020  (1)
• September 2020  (2)
• August 2020  (1)
• June 2020  (2)
• May 2020  (1)
• April 2020  (1)
• February 2020  (1)
• January 2020  (1)
• November 2019  (2)
• September 2019  (2)
• August 2019  (2)
• July 2019  (2)
• May 2019  (1)
• March 2019  (3)
• February 2019  (2)
• January 2019  (2)
• December 2018  (1)
• October 2018  (1)
• September 2018  (1)
• August 2018  (3)
• July 2018  (3)
• June 2018  (2)
• March 2018  (3)
• February 2018  (1)
• January 2018  (1)
• December 2017  (2)
• November 2017  (1)
• October 2017  (3)
• September 2017  (1)
• August 2017  (2)
• July 2017  (1)
• June 2017  (3)
• May 2017  (2)
• April 2017  (3)
• March 2017  (3)
• February 2017  (3)
• January 2017  (4)
• December 2016  (2)
• November 2016  (2)
• October 2016  (5)
• September 2016  (2)
• August 2016  (5)
• July 2016  (4)
• June 2016  (5)
• May 2016  (2)
• April 2016  (3)
• March 2016  (6)
• February 2016  (4)
• January 2016  (4)
• December 2015  (4)
• November 2015  (5)
• October 2015  (4)
• September 2015  (4)
• August 2015  (5)
• July 2015  (4)
• June 2015  (2)
• May 2015  (3)
• April 2015  (6)
• March 2015  (8)
• February 2015  (10)
• January 2015  (17)
• ad hoc fallacies
• alternative medicine
• anecdotal evidence
• anti vaccine arguments
• appeal to antiquity fallacies
• appeal to authority fallacies
• appeal to emotion fallacies
• appeal to nature fallacies
• argument from ignorance fallacies
• Bad arguments
• burden of proof
• cherry picking
• conflict of interest
• creationism
• evaluating evidence
• global climate change
• logical fallacies
• natural selection
• peer-reviewed studies
• post hoc ergo propter hoc fallacies
• rules of logic
• scientific consensus

• Already have a WordPress.com account? Log in now.
• Subscribe Subscribed
• Copy shortlink
• Report this content
• View post in Reader
• Manage subscriptions
• Collapse this bar

• EXPLORE Random Article
• Happiness Hub

How to Explain the Difference Between Theory, Law, and a Fact

Last Updated: December 2, 2021 References

This article was co-authored by Bess Ruff, MA . Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group. This article has been viewed 155,441 times.

Within scientific communities, “theory,” “law,” and “fact” are technical terms which have distinct and complex meanings. Many people who do not have a scientific background—including students in introductory science classes in high school and colleges—do not have a firm understanding of the differences between these 3 terms. Many adults are also unaware of the distinctions between these 3 terms, and can benefit from a polite, conversational explanation. This article will help you understand and explain the differences between proper scientific uses for each of the three terms.

Explaining the Difference between Scientific Theory and Law

• Laws have never been refuted (hence their relatively small number) and are not explanations; they are descriptions and are often stated through relatively simple mathematical equations.
• Scientific laws, despite their formality, can change or have exceptions as scientific understandings of phenomena evolve. [2] X Research source

• As an example, the Law of Gravity has been known in the scientific community since the late 17th century. The law describes the natural phenomenon of gravity, but does not provide an explanation as to how and why gravity functions.

• A theory builds from initial hypotheses (educated guesses) and can be revised in accordance with the development of a scientific understanding of a phenomena’s cause.
• A theory is confirmed by all available evidence such that it can be used to predict new, as yet unobserved phenomena.

• For example, the scientific Theory of Natural Selection corresponds with the Law of Evolution. [5] X Research source While the law states an observed natural phenomena (life forms develop new characteristics based on external circumstances), the theory describes how and why this happens.

Explaining the Difference between Scientific Law and Fact

• While facts can be scientifically refuted or may not be consistent across time and place, they are held as true until they have been proven wrong.

• When explaining a scientific fact, start with a point of general observation.
• For example, begin your explanation by saying something like, “it is always bright outside at noon.” This is a fact in that it describes a state of nature—however, this statement may not be true in Antarctica or Greenland, where darkness lasts throughout the day in certain seasons.
• Explain how this will lead to a revision of the scientific fact: “within certain degrees of latitude, it is always bright outside at noon.”

• Facts are less formal than laws, and are not seen as an “official” definition of a phenomenon that occurs or of the reason that something happens.
• Facts are more localized and generalize less than laws. Explain that, if the Law of Evolution describes the way that species throughout the world evolve over time, a scientific fact related to evolution (and natural selection) could be: “giraffes with long necks can reach more leaves than giraffes with short necks.”

• For example, scientific theories do not develop into scientific laws. To explain the difference, focus on this distinction: laws describe phenomena, theories explain phenomena, and facts describe observations.

Explaining Scientific Theories, Laws, and Facts in the Classroom

• A theory is worth very little if it doesn't correctly predict all known evidence.
• Theories are subject to changes as new evidence becomes available. (Most theories that you will discuss in a high school science class are well-confirmed and are unlikely to be revised in any significant sense.)

• The theory of relativity: that the laws of physics are the same for all observers
• The theory of evolution by natural selection: that the observed changes in species occur due to selection of well adapted specimens over less well adapted specimens.
• Big Bang theory: that the universe began as an infinitely small point that underwent expansion to form the universe as we know it today.

• For example, we know that the germ theory of illness is a fact because we can take bacteria from someone suffering from an illness, look at that bacteria under a microscope, and then inject that bacteria into another individual, who will then get that same illness.
• We know that the Earth is round because we can travel due west and eventually end up where we started from.

• Ancient peoples noticed peculiar points of light that “wandered” among their background. (We now know these to be the planets.)
• The planets moved through the sky because they, like the Earth, were orbiting around the sun, each at different speeds, different distances from the Sun.
• Nicolaus Copernicus is generally considered to be the first to propose this theory, and supported his theory with hard evidence, but ancient cultures stumbled upon this through speculation.
• We now consider this a fact because we have sent many craft to these planets and can predict their motions to a very high precision. Of course, our predictions come from the theory (and the laws underlying that theory).

• Newton's Law of heating and cooling: the change in temperature of two bodies in thermal contact is proportional to their difference in temperature.
• Newton's Laws of motion: statements about how large objects made of atoms behave when moving at low speeds relative to each other.
• The Laws of Thermodynamics: statements about entropy, temperature, and thermal equilibrium.
• Ohm's Law: the voltage across a purely resistive element is equal to the current through the element times its resistance.

• For example, one must infer that the derived laws actually predict the facts. Accumulating all of the previous forms of knowledge, a scientist makes a general statement to explain all the evidence.
• Other scientists reaffirm the facts and use the theory to make predictions and obtain new facts.

Expert Q&A

You Might Also Like

• ↑ http://lifehacker.com/the-difference-between-a-fact-hypothesis-theory-and-1732904200
• ↑ http://www.livescience.com/21457-what-is-a-law-in-science-definition-of-scientific-law.html
• ↑ https://ncse.com/library-resource/definitions-fact-theory-law-scientific-work
• ↑ http://futurism.com/hypothesis-theory-or-law/
• ↑ https://pseudoastro.wordpress.com/2008/12/21/terminology-what-scientists-mean-by-fact-hypothesis-theory-and-law/

About this article

Did this article help you?

• About wikiHow
• Terms of Use
• Privacy Policy
• Do Not Sell or Share My Info
• Not Selling Info

• Science, Tech, Math ›

Hypothesis, Model, Theory, and Law

Dorling Kindersley / Getty Images

• Physics Laws, Concepts, and Principles
• Quantum Physics
• Important Physicists
• Thermodynamics
• Cosmology & Astrophysics
• Weather & Climate

• M.S., Mathematics Education, Indiana University
• B.A., Physics, Wabash College

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?

• Science Notes Posts
• Contact Science Notes
• Todd Helmenstine Biography
• Anne Helmenstine Biography
• Free Printable Periodic Tables (PDF and PNG)
• Periodic Table Wallpapers
• Interactive Periodic Table
• Periodic Table Posters
• Science Experiments for Kids
• How to Grow Crystals
• Chemistry Projects
• Fire and Flames Projects
• Holiday Science
• Chemistry Problems With Answers
• Physics Problems
• Unit Conversion Example Problems
• Chemistry Worksheets
• Biology Worksheets
• Periodic Table Worksheets
• Physical Science Worksheets
• Science Lab Worksheets
• My Amazon Books

Scientific Law Definition and Examples

A scientific law is a statement or mathematical equation that describes or predicts a natural phenomenon. It does not explain why or how a phenomenon occurs. Another name for a scientific law is a law of nature or law of science . All scientific laws are based on empirical evidence and the scientific method. In science, an assertion can be disproven, but never proven, so it’s possible for a scientific law to be revised or disproven by future experiments. In contrast, a mathematical theorem or identity is proven to be true.

Examples of Scientific Laws

There are laws in all scientific disciplines, although primarily they are physical laws. Here are some examples:

• Beer’s law
• Dalton’s law of partial pressures
• Ideal gas law
• Kepler’s laws of planetary motion
• Law of conservation of mass
• Law of conservation of energy
• Law of conservation of momentum
• Law of reflection
• Laws of thermodynamics
• Newton’s law of universal gravitation
• Newton’s laws of motion

Difference Between a Scientific Law and Scientific Theory

Both scientific laws and scientific theories are based in the scientific method and are falsifiable. However, the two terms have very different meanings. A law describes what happens, but does not explain it. A theory explains how or why something works.

For example, Newton’s law of universal gravitation describes what happens when two masses are a given distance apart. The law can be written as a mathematical equation [F = G(m 1 m 2 /r 2 )] and used to make predictions and calculations. However, the law does not explain how gravity works or why two masses are attracted to one another. Scientists didn’t really have an explanation for gravity until Einstein’s theory of general relativity, which continues to be revised as we understand more about the nature of spacetime.

As another example, Hubble’s law of Cosmic Expansion (velocity = Hubble constant x distance) describes the movement of galaxies away from each other. It does explain why this occurs. The Big Bang Theory is one of the theories that explains why galaxies move apart, but the theory does not offer a formula for calculating this motion.

Can a Hypothesis or Theory Become a Law?

A hypothesis , theory, and law are all parts of scientific inquiry, but one never becomes another . They are different things. A hypothesis never becomes a theory, no matter how many experiments support it, because a hypothesis is simply a prediction about how one variable responds when another is changed. A theory takes into account the results of many experiments, testing different hypotheses. A theory explains how something works. Like a theory, a law draws on the results of repeated observations and experiments. But, a law states in words or mathematical equations what happens. Laws don’t explain why.

• Barrow, John (1991). Theories of Everything: The Quest for Ultimate Explanations . ISBN 0-449-90738-4.
• Feynman, Richard (1994). The Character of Physical Law (Modern Library ed.). New York: Modern Library. ISBN 978-0-679-60127-2.
• Gould, Stephen Jay (1981). “ Evolution as Fact and Theory “. Discover . 2 (5): 34–37.
• McComas, William F. (2013). The Language of Science Education: An Expanded Glossary of Key Terms and Concepts in Science Teaching and Learning. Springer Science & Business Media. ISBN 978-94-6209-497-0.

Related Posts