I have to admit, I am still confused. Could someone explain to me the difference between a theory and a law?

Question

I don't know how often I've seen in here someone trying to explain to us what a "theory" is, in science, by telling us that we can test a scientific theory by falling off the roof...
So, how is citing "The Law of Gravity" giving us any information about what a "scientific theory" is?
And how does that have anything to do with the skeletons in the closet?
Or, more to the point, the empty hangers where skeletons ought to be??

Answer 1

This is a good question, sadly few people seem to understand the difference (including everbody but ooz above me and duck and drac below me). Scientific laws describe physical phenomena (often in terms of math) and they have no exceptions. Scientific theories try to explain how these phenomena occur, or what causes them. Simply put: law = what, theory = how. A good example would be the gas laws and kinetic molecular theory. The gas laws describe what happens to gasses when you change the volume, the temperature, the pressure, or the amount of gas in a container. The gas laws have no exceptions. Kinetic molecular theory explains these laws in terms of molecules and makes testable predictions based on the idea that a gas is made of molecules; predictions not made by the laws themselves. Kinetic molecular theory may be wrong, but it has predictive value and is a very successful theory. If new evidence were to arise that discredited kinetic molecular theory, scientists would either modify the theory to account for the new evidence, or discard it altogether and come up with a new theory. The new theory would still have to explain the gas laws and the new evidence, and it would have to make testable predictions so that it could be verified.

Answer 2

Some crazy answers above! A law is a statement that summarizes many observations. A theory is a conceptual framework and set of ideas for understanding and thinking about observations. So one big difference is that a Law is usually a lot shorter than a Theory! A Law is a single-sentence, short statement of fact, often expressible as a mathematical equation, that has been proven by experiment. It is often PART OF a theory. A theory is more like a "story" (hopefully a true story!). It's a conceptual framework; it introduces and defines a number of concepts and explains their interrelationships, and explains how experimental results can be viewed in terms of those concepts. A theory may (or may not) include one or more statements that eventually become Laws. Example: Isaac Newton put forth a Theory of Gravitation. It introduces the idea that there is an attractive force between all bodies in the universe. Part of Newton's theory is the Law of Universal Gravitation, which is expressed as "F = GMm/R²" Today, another way to view the motions of massive bodies around each other is through the Theory of Relativity. For some purposes it's a preferable "story" because it addresses some experimental observations that Newton's theory doesn't. For many purposes, Newton's "story" is preferable because it addresses MOST ordinary cases and the math is a lot simpler. But even though Einstein's theory is more comprehensive, Newton's Law of Gravitation is still a Law, because it's still an extremely useful and accurate equation.

Answer 3

You know, people get pretty worked up about language.

It's important that everyone uses the same definition of a word, because otherwise communication becomes difficult. But if everyone is using a new definition of a word already, there's no point in defending an old definition to the death. So, before I answer your question, I'd just like to remind you to keep the person you're talking to in mind; the way they use the word "theory" may not be the same as the way scientists use the word, or the way a Babtist preacher might use the word.

To answer your question, this is the difference for most people:

Hypothesis: Something I came up with myself to explain the world around me, that I haven't tested yet

Philosophy: A hypothesis that never needs, or isn't intended, to be tested

Theory: A hypothesis that's been tested, what we learned from testing the hypothesis, and most importantly, a general rule that explains the results. For example, if I saw four eggs, three of them hatched, and chickens came out, I could make this hypothesis:

The next thing that hatches is probably a chicken

If I waited around, and saw the fourth egg hatch, and it was indeed a chicken, I could make the following theory

When a nest had four eggs, and three of them hatched chicks, the fourth hatched a chick as well. Therefore:
Nests that hatch chicks will tend to continue to hatch chicks.

Of course, there's a difference between a theory, and an /accepted/ theory. To get your theory accepted, you've got to publish it for peer review. And using my example, I'd probably have to watch a lot more chicks hatch, and possibly some other types of animal as well.

Law: The main difference between a law and a theory, is that a law usually has an "empirically determined constant" associated with it. That's a fancy way of saying that we can prove that there's a specific number (the speed of light, for example, or things falling toward the earth at exactly 32 feet per second per second) that we can always get using the law (which is usually also an equation), and that number is always right no matter how many times or ways we test it.

While my chicken hatching theory will probably never become a law, if it did, this is what it would look like:
"Given an egg(E) from a particular species(s), and a nest(N) from a particular species, the animals that hatch(A), will probably be of the same species, or
if Ns = C(E), and E -> A, then Ns = As,
where C is any constant (any number of eggs, in other words)"

Of course, since there isn't really an empirically defined constant, and it doesn't really explain anything about the world, this wouldn't ever really work as a law.

The following is the list that Wikipedia has of scientific laws we've got so far:
-Newton's 3 Laws of Motion
-Archimede's Principle
-Kepler's 3 Laws of Planetary Motion
-Newton's Law of Universal Gravitation
-Newton's Law of Cooling
-Boyle's Law
-The Laws of Thermodynamics
-Joule's First and Second Laws
And, in some circles,
-Heisenberg's Uncertainty Principle (Wikipedia says so, anyway)

Answer 4

Actually gravity is still a theory too. And there have been physicists arguing against some of Newton's equations for more than a decade. There are indications that gravity may not be constant across the entire universe. It isn't widely accepted, but there is some scientific disagreement Far more than there is for evolution.

A scientific law describes an observed behavior within a certain set of parameters. The laws do break down when you get outside of those parameters.

A scientific theory describes the mechanism behind the behavior.

No amount of evidence will ever move a theory to a law. So as it applies to evolution. There is a scientific Law of Fossil Succession that describes the way they lay in the geology. And there is the Theory of Evolution that proposes how they got that way. Creationism is inconsistent with fossil succession.

Answer 5

I have no idea about that last stuff but a scientific law is a rock solid, proven, tested a thousand times fact. There is little room to argue a scientific law. For instance the Law of Gravity you mentioned. If you jump off your roof you fall, you throw a ball it comes back down sooner or later, objects are drawn to other objects of greater mass. Proven facts, completely inarguable.

A scientific theory is something that has been more or less proven by being tested a lot, observed and agreed upon by science in general. The difference is that it isn't solidified, there isn't much room for adjustment but it can still change a little as our understanding progresses. The Theory of Evolution for example has been tested in laboratories and observed both in contained environments and in nature and nearly all of the scientific community agrees it is a fact. However our understanding of it is and most likely always will be incomplete therefore it will remain theory until there are no errors left in it.

Last is a hypothesis, which is a nearly unsupported, untested idea. Creationism is considered a hypothesis. It is untestable in a general sense, unobservable, and hardly any part of the scientific community believes it is fact. However, because true science will not disregard any idea that cannot outright be proven wrong it remains a hypothesis despite everything against it, meaning it is a possibility even though it is a slim possibility.

Answer 6

A scientific theory can be thought of as a "model" whose imaginary properties you can test against the real world; insofar as they correspond, you've got yourself a good theory. But you can never rule out the possibility of the real world presenting you with data that doesn't jibe with your model, regardless of how much corroborating data you've already accumulated.

As for the difference between a "theory" and a "law," I can't do better than oozɐƃ ʇɐǝɹƃ ǝɥʇ above: "A scientific law describes an observed behavior within a certain set of parameters. The laws do break down when you get outside of those parameters. A scientific theory describes the mechanism behind the behavior."

But see also DuckPhup, Gman and science geek. If you're actually interested in knowing the difference.

Answer 7

A Law is simply smaller. Dealing with a smaller subject within a larger scope of things. To be accorded law-like status a wide variety of these conditions should be known, i.e. the law has a well documented history of successful replication and extension to new conditions. Ideally boundary conditions, where the law fails, should also be known. A scientific law concerns the physical or social world, it therefore must have empirical content and therefore be capable of testing and potentially falsifiable. Analytic statements that are true or false by logic alone are not scientific laws, though may feature as part of scientific theories.


The word theory has a number of distinct meanings in different fields of knowledge, depending on their methodologies and the context of discussion. In common usage, people often use the word theory to signify a conjecture, an opinion, or a speculation. In this usage, a theory is not necessarily based on facts; in other words, it is not required to be consistent with true descriptions of reality. True descriptions of reality are more reflectively understood as statements which would be true independently of what people think about them. In this usage, the word is synonymous with hypothesis.

In science, a theory is a mathematical or logical explanation, or a testable model of the manner of interaction of a set of natural phenomena, capable of predicting future occurrences or observations of the same kind, and capable of being tested through experiment or otherwise falsified through empirical observation. It follows from this that for scientists "theory" and "fact" do not necessarily stand in opposition. For example, it is a fact that an apple dropped on earth has been observed to fall towards the center of the planet, and the theories commonly used to describe and explain this behaviour are Newton's theory of universal gravitation (see also gravitation), and general relativity.

Think of it this way... Scientific theories generally contain many Laws but Theories talk about all the Laws pertaining to the subject while the Law talks about only one.

For example.... We all know that part of Evolution is Natural Selection. There are Laws to support Natural Selection, such as Gregor Mendels "Laws of Inheritance" which deals with the fact that genes are passed from people to their offspring and how it works.

Genetic Drift is also part of Evolution, and it contains such Laws as the The Hardy-Weinberg which assumes that in the absence of selection or other evolutionary forces, absolutely no gene frequency change occurs during reproduction. This would be true in an infinitely large population; under these conditions, selection would be completely predictable and deterministic.

However, this is only approximately true in real populations of finite size.

This, a Scientific Theory has many many Laws. But a Scientific Theory itself deals with ALL information pertaining to a larger subject. In this case, such things as Genetic Drift and Natural Selection as well as Speciation, Genetic Flow, Mutation, and Adaptation which have their own sets of Laws that I haven't posted because you probably won't read them anyway.

Its like Musical Theory. We all know music is not a Theory right? Its not a guess. It exists. Musical Theory pertains to the Laws that deal with rhythm, harmony, melody, structure, and texture.

Thus a Scientific Theory is not a guess. Its simply the broadest possible term applied to many different Laws at a given moment.

If I were to start talking to people about allele frequency, they'd have no idea what I'm saying at all. Its much easier to talk to a lay person about Evolution in general because they then have some idea of what I'm talking about.

You cannot test a scientific theory by falling off a roof. Whoever said that is an idiot.

The Law of Gravity and Gravitational Theory are actually different things. The Laws of Gravity (such as Newtons Law of Universal Gravitation which deals with Every single point mass attracts every other point mass by a force pointing along the line combining the two. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses), are actually a much smaller portion of the information available on Gravity. The entirety of the information of Gravity is called a Theory, even though it actually isn't.

It has nothing to do with skeletons in closets. What an odd thing to say.

Edit: rofl.... so I give you the real, unbiased description of the difference between a Scienfitic Theory and a Law and get a thumbs down for it. Boy, you people are really desperate if you can't handle the truth you'll find in a dictionary.

Edit: Yes, its very amusing that they can't handle the truth.... and a little disturbing too. The odd thing that I can't really understand is that someone with no scientific knowledge beyond the basics they learned in high school (if that) thinks they know more than a person with university and college degrees. I thought the world placed the importance on education. Guess not.

Answer 8

Ok...Law, a scientific theory that has been tested beyond a reasonable doubt as fact, but can still be proven wrong if there is sufficent evidence of the Law being false. Theory...scientific hypothesis that has been tested and is widely held to be fact, more testing is required for it to become a Law...as for the reason why people say to jump off a roof to prove Gravity, well, you say Evolution isn't real, it's just a theory, Gravity is both Theory and Law...so that's why, we say for you to jump off a roof, it's only a theory. Hope I helped.

Answer 9

A theory is a "model" or concept that explains a wide range of experimental observations and hypotheses. It must be able to predict future happenings. Evolution does both. A theory can be disproven, but it takes CONSIDERABLE evidence to disprove it. Evolution is a fact, but natural selection is theoretical, meaning that it is not the only mechanism for evolution.

A law is usually a mathematical equation that has almost never been disproven. A law, too, explains a wide range of phenomena, but it more "perfect" than a theory. It is VERY DIFFICULT for a hypothesis or a theory to be recognized as a law. The three rules of thermodynamics are laws.

Astronomy: Big Bang Theory
Biology: Cell theory — Evolution
Chemistry: Atomic theory — Kinetic theory of gases
Climatology: Theory of Global Climate Change (due to anthropogenic activity)
Computer science: Algorithmic information theory — Computation theory
Economics: Decision theory
Education: Constructivist theory — Critical pedagogy theory — Education theory — Emotional education theory — Multiple intelligence theory — Progressive education theory
Engineering: Circuit theory — Control theory — Signal theory — Systems theory
Film: Film Theory
Games: Game theory — Rational choice theory
Geology: Plate tectonics[2]
Humanities: Critical theory
Literature: Literary theory
Mathematics: Catastrophe theory — Category theory — Chaos theory — Graph theory — Knot theory — Number theory — Probability theory — Set theory
Music: Music theory
Philosophy: Proof theory — Speculative reason — Theory of truth — Type theory — Value theory — Virtue theory
Physics: Acoustic theory — Antenna theory — General relativity — Special relativity — Theory of relativity — Quantum field theory
Planetary science: Giant impact theory
Visual Art: Aesthetics — Art Educational theory — Architecture — Composition — Anatomy — Colour_theory — Perspective — Visual_perception — Geometry — Manifolds
Sociology: Sociological theory — Social theory — Critical theory
Statistics : Extreme value theory
Theatre : Theory relating to theatrical performance.
Other: Obsolete scientific theories — Phlogiston theory

Answer 10

The term Law was used to imply something that was universal, ie applied throughout space and time, hence laws relating to physics. Biological theories were assumed to be local as they would not necessarily apply through the universe.

Having said that we no longer use the term 'Law' in science, haven't for a couple of hundred years, everthing is a theory now, whimsical terms like 'Moores law' notwithstanding.

And for emphasis, Newtons 'laws' of motion are false while Einsteins 'theory' of relativity is true.