I'm just trying to speak properly and the definitions of fact, hypothesis, theory and law are quite mixed in my head.

Some background

The following are not perfect definitions but some ideas.

  • Facts: observations (it is much more complex as it depends on what we considered true previously, on perception, and so on. I'm not sure if it depends on culture.)
  • Hypothesis: explanation of a fact. It can be generally disproven or proven for some particular cases using the scientific method.
  • Theory: deep hypothesis, can be proven or disproven in same way than a hypothesis.
  • Law: general description of observations.


Does a law become a theory if the hypothesis are confirmed by experience?

If it is so, there are many theories that should be laws (as quantum theory) but they dont, so I'm quite puzzled.

Any improvement/completion on the previous ideas, links or essays to read are welcome.

  • Scientific laws are what Pythagoreans called 'knowledge'. That is... They are usually simple mathematical statements which have been proven either back to a priory knowledge or beyond all doubt by peer corroborated experiment. Like all 'knowledge' that science uncovers... Laws are not sacred and can be overturned.. we know for example that some of Newton's laws are not quite correct.. but they are still referred to as laws for various reasons.
    – Richard
    Commented Dec 1, 2018 at 22:51
  • A theory becomes a law when there are social costs to breaking the law. Commented Dec 3, 2018 at 19:27

6 Answers 6


See Laws of Nature : usually, scientific laws are general and have explanatory power.

Scientific theories are quite complex sets of statements, made of facts (or data), laws, hypothesis, etc.

See also Theory and Observation in Science.

Thus, e.g. Quantum mechanics is a theory and not a law or hypothesis.

In conclusion, regarding the question :

Can a theory become a law ?

if we agree on the above terminology, a law is part of a theory.

Maybe useful :


According to the Collins dictionary a theory is: a set of hypotheses related by logical or mathematical arguments to explain and predict a wide variety of of connected phenomena in general terms.

A law is: a general principle formula, or rule describing a phenomena in mathematics, science, philosophy, etc.

The main point is that a theory explains something, while a law just describes something. For example the theory of evolution by natural selection explains how organisms adapt while the law of conservation of mass just describes a fact (not why it is the case). So in general a theory does not become a law and vice versa they are two different things.


Laws are typically things which can be derived from a remarkably small number of mathematical assumptions. However, the lines between these terms are forever blury, so you will likely not find a crisp delineation between them.

As an example, consider Hooke's Law. Hooke's Law states that the amount a spring stretches is proportional to the forces on it. In mathematical notation, we write this as F=-kx. No spring in the history of mankind has actually obeyed this rule. This rule describes what we call an "ideal" spring. Real springs have all sorts of other terms that appear to deal with non-linear effects. So in the case of Hooke's Law, its a law describing a physical behavior that no real object upholds!

Contrast that with the Theory of Everything which physicists are trying to arrive at. Its goal is to describe everything that occurs in the universe, and yet it only gets the title of "theory."

Darwin's treatise on species is most properly know as his Theory of Evolution. But in practice, many people choose to treat it as a perfect invariant idea which is more associated with the term "law."

We also have fun with gravity. Newton's Law of Universal Gravitation is called a law, but we now know it isn't true. For a more accurate model of how the universe works, we turn to the General Theory of Relativity. In this case, the theory is the more universally correct version than the law!



  • Fact, a piece of information about reality that is considered to be accurate

  • Hypothesis, a speculation about how reality works, but with no or incomplete facts to verify that it is accurate

  • (Scientific) Theory, a hypothesis that has been verified to be accurate with the help of facts.

    Note how this relates very closely to "fact".

  • Law of nature, synonym for "(Scientific) Theory"


Both terms are at different levels.

Previously, you should remark that any discipline has 3 axis: science, technique, art (Mario Bunge).

A theory is a type of knowledge: it is ideal, and could or not be related to facts (the Big Bang is a theory, although we cannot prove it; quantum mechanics is another theory that has been proven). It can or cannot be scientific, according to the method of knowledge development (science is created using the scientific method). But it is static knowledge, not necessarily related to other knowledge.

A law is not related to knowledge, but to causality: laws are relations between facts. Scientific laws describe the causal relationship between facts (e.g. the laws of thermodynamics describe the relationships between energy and mass; the second law says that if there's energy inside a thing, it tends to spread across the thing, you see? causality, if/then; action/reaction, etc.). Social laws determine the relationships between behaviors, in order to survive. For example, someone kills, then he must be isolated, so he stops killing and the group increases the probability of survival. Consider that causality is not a physical fact, but mental.

Quantum mechanics is usually not expressed as laws, since we don't understand them quite well. We have a theory that describes the facts perfectly, but we don't understand them (how can the past be changed? what does it mean? how can a thing have two states (which reduces to what is a thing?)? how can information be transferred faster than the speed of light?). Since causality is a mental feature, we cannot formulate causal relationships between facts we don't understand.


In general, the terms 'theory,' 'hypothesis.' and 'law' all have the same meaning. Most of the theories that are called laws (e.g. Newton's laws of motion, the Biot-Savart Law) were so named prior to the collapse of classical physics when it was almost universally believed that the theories were, in fact, the actual laws of nature. Today, we are not so confident; so our theories are typically just called theories. I.e. we don't call Schrodinger's equation 'Schrodinger's law.'

As far as the 'hypotheses' vs 'theory' distinction goes, feel free to use the two terms interchangeably. Many people believe (incorrectly) that a hypothesis is a theory that hasn't been tested. This is not the case; there are many theories that either have not been tested and/or cannot be tested (e.g. string theory). But typically, in normal speak, 'hypotheses' tends to be a weaker term that might imply that the theory is more of a guess.

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