What is a Scientific Theory? Scientific Law? Scientific Hypothesis? (updated December 5 2022)

What is a Scientific Theory? Scientific Law? Scientific Hypothesis? These are important and common questions.

A lot of information from various sources, discussing the Laws of Physics and other matters.

A scientific law or scientific principle is a concise verbal or mathematical statement of a relation that expresses a fundamental principle of science, like Newton's law of universal gravitation. A scientific law must always apply under the same conditions, and implies a causal relationship between its elements.

A law differs from a scientific theory in that it does not posit a mechanism or explanation of phenomena: it is merely a distillation of the results of repeated observation. As such, a law limited in applicability to circumstances resembling those already observed, and is often found to be false when extrapolated.

Honderich, Ted, ed., "Laws, natural or scientific", Oxford Companion to Philosophy, Oxford: Oxford University Press, pp. 474–476

 Ehrenberg, Andrew S C , "Even the Social Sciences Have Laws," Nature, 365 (30), 385.

From Encarta

Scientific Law, in science, principles that are taken to be universally applicable. Laws (for instance, Boyle's law and Newton's laws of motion) form the basic theoretical structure of the physical sciences, so that the rejection of a law by the scientific community is an extremely rare event. On occasion a law may be modified, as was the case when Albert Einstein showed that Newton's laws of motion do not apply to objects traveling at speeds close to that of light.

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A nice explanation from a Teacher:

LAW
1) An empirical generalization; a statement of a biological principle that appears to be without exception at the time it is made, and has become consolidated by repeated successful testing; rule (Lincoln et al., 1990)
2) A theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by a statement that a particular phenomenon always occurs if certain conditions be present (Oxford English Dictionary as quoted in Futuyma, 1979).
3) A set of observed regularities expressed in a concise verbal or mathematical statement. (Krimsley, 1995).
THEORY
1) The grandest synthesis of a large and important body of information about some related group of natural phenomena (Moore, 1984)
2) A body of knowledge and explanatory concepts that seek to increase our understanding ("explain") a major phenomenon of nature (Moore, 1984).
3) A scientifically accepted general principle supported by a substantial body of evidence offered to provide an explanation of observed facts and as a basis for future discussion or investigation (Lincoln et al., 1990).
4) 1. The abstract principles of a science as distinguished from basic or applied science. 2. A reasonable explanation or assumption advanced to explain a natural phenomenon but lacking confirming proof (Steen, 1971). [NB: I don't like this one but I include it to show you that even in "Science dictionaries" there is variation in definitions which leads to confusion].
5) A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles or causes of something known or observed. (Oxford English Dictionary, 1961; [emphasis added]).
6) An explanation for an observation or series of observations that is substantiated by a considerable body of evidence (Krimsley, 1995).

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Scientific Laws, Hypotheses, and Theories

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:

Scientific Law: This is a statement of fact meant to explain, in concise terms, an action or set of actions. It is generally accepted to be true and univseral, 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.

Theory: A theory is more like a scientific law than a hypothesis. 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. One scientist cannot create a theory; he can only create a hypothesis.

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 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 governs a single action, whereas a theory explains an entire group of related phenomena.

Theories can be tweaked, but they are seldom, if ever, entirely replaced.
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From About.com

Words have precise meanings in science. For example, 'theory', 'law', and 'hypothesis' don't all mean the same thing. Outside of science, you might say something is 'just a theory', meaning it's supposition that may or may not be true. In science, a theory is an explanation that generally is accepted to be true. Here's a closer look at these important, commonly misused terms. 

 

Hypothesis
A hypothesis is an educated guess, based on observation. Usually, a hypothesis can be supported or refuted through experimentation or more observation. A hypothesis can be disproven, but not proven to be true.

 

Theory
A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven. Basically, if evidence accumulates to support a hypothesis, then the hypothesis can become accepted as a good explanation of a phenomenon. One definition of a theory is to say it's an accepted hypothesis.

Law
A law generalizes a body of observations. At the time it is made, no exceptions have been found to a law. Scientific laws explain things, but they do not describe them. One way to tell a law and a theory apart is to ask if the description gives you a means to explain 'why'.
There is no 'proof' or absolute 'truth' in science. The closest we get are facts, which are indisputable observations. Note, however, if you define proof as arriving at a logical conclusion, based on the evidence, then there is 'proof' in science. I work under the definition that to prove something implies it can never be wrong, which is different. If you're asked to define hypothesis, theory, and law, keep in mind the definitions of proof and of these words can vary slightly depending on the scientific discipline. What is important is to realize they don't all mean the same thing and cannot be used interchangeably.

See More About:

• chemistry definitions
• hypothesis
• scientific laws

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Scientific Hypothesis, Theories and Laws

The principles and theories of science have been established through repeated experimentation and observation and have been refereed through peer review before general acceptance by the scientific community. Acceptance does not imply rigidity or constraint, or denote dogma. Instead, as new data become available, previous scientific explanations are revised and improved, or rejected and replaced. Science is a way of making sense of the world, with internally-consistent methods and principles that are well described. There is a progression from a hypothesis to a theory using testable, scientific laws. Only a few scientific facts are natural laws and many hypotheses are tested to generate a theory. Find out how scientific hypotheses, theories and laws describe the natural world.

 

What is a hypothesis?

A hypothesis is an idea or proposition that can be tested by observations or experiments, about the natural world. In order to be considered scientific, hypotheses are subject to scientific evaluation and must be falsifiable, which means that they are worded in such a way that they can be proven to be incorrect.

 

What is a scientific theory?

To scientists, a theory is a coherent explanation for a large number of facts and observations about the natural world.
A theory is:

• Internally consistent and compatible with the evidence
• Firmly grounded in and based upon evidence
• Tested against a wide range of phenomena
• Demonstrably effective in problem-solving

In popular use, a theory is often assumed to imply mere speculation, but in science, something is not called a theory until it has been confirmed over many independent experiments. Theories are more certain than hypotheses, but less certain than laws. The procedures and processes for testing a theory are well-defined within each scientific discipline.

What is a scientific law?

A scientific law is a description of a natural phenomenon or principle that invariably holds true under specific conditions and will occur under certain circumstances.

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SCIENTIFIC LAWS and THEORIES

Here are a couple of definitions of each word.
LAW
1) An empirical generalization; a statement of a biological principle that appears to be without exception at the time it is made, and has become consolidated by repeated successful testing; rule (Lincoln et al., 1990)
2) A theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by a statement that a particular phenomenon always occurs if certain conditions be present (Oxford English Dictionary as quoted in Futuyma, 1979).
3) A set of observed regularities expressed in a concise verbal or mathematical statement. (Krimsley, 1995).

THEORY
1) The grandest synthesis of a large and important body of information about some related group of natural phenomena (Moore, 1984)
2) A body of knowledge and explanatory concepts that seek to increase our understanding ("explain") a major phenomenon of nature (Moore, 1984).
3) A scientifically accepted general principle supported by a substantial body of evidence offered to provide an explanation of observed facts and as a basis for future discussion or investigation (Lincoln et al., 1990).
4) 1. The abstract principles of a science as distinguished from basic or applied science. 2. A reasonable explanation or assumption advanced to explain a natural phenomenon but lacking confirming proof (Steen, 1971). [NB: I don't like this one but I include it to show you that even in "Science dictionaries" there is variation in definitions which leads to confusion].
5) A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles or causes of something known or observed. (Oxford English Dictionary, 1961; [emphasis added]).
6) An explanation for an observation or series of observations that is substantiated by a considerable body of evidence (Krimsley, 1995).

Some scientists will tell you that the difference between them is that a law describes what nature does under certain conditions, and will predict what will happen as long as those conditions are met. 

A theory explains how nature works.  Others delineate law and theory based on mathematics -- Laws are often times mathematically defined (once again, a description of how nature behaves) whereas theories are often non-mathematical. Looking at things this was helps to explain, in part, why physics and chemistry have lots of "laws" whereas biology has few laws (and more theories). In biology, it is very difficult to describe all the complexities of life with "simple" (relatively speaking!) mathematical terms. 

Regardless of which definitions one uses to distinguish between a law and a theory, scientists would agree that a theory is NOT a "transitory law, a law in waiting". There is NO hierarchy being implied by scientists who use these words. That is, a law is neither "better than" nor "above" a theory. From this view, laws and theories "do" different things and have different roles to play in science. Furthermore, notice that with any of the above definitions of law, neither scientists nor nature "conform" to the law. In science, a law is not something that is dictated to scientists or nature; it is not something that a scientist or nature has to do under threat of some penalty if they don't conform.
source

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Scientific law

true or (more weakly understood) well confirmed or established. On realist conceptions the laws of science are generally regarded as expressing the [causal} laws according to which all occurs, or by which all is governed. See cause, determinism.
[Philosophical Glossary]
<2001-06-22>

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Scientific Laws and Theories

A scientist seeks to understand both how and why nature works. But scientists are far more successful at understanding the "hows" than the "whys". We are good at recognizing patterns in nature and predicting them. But our understanding of the complexities of nature has just begun. Although we would always like to know why some phenomenon occurs in nature, extracting this information can be very difficult. On the other hand, discovering how nature works through the patterns and order revealed through scientific experiments can lead to general laws from which predictions about the phenomenon in question can be made. It is important to understand at the outset that science does not require an answer to the question of why something happens, only how. The degree of success of a scientific law, theory or model is judged by the accuracy that they can predict phenomena.

 

A scientific law is a rule or a set of rules which generalizes the behavior of some phenomenon in nature. For example, Newton's First Law of Motion states that every object either remains at rest or in continuous motion with constant speed unless acted upon by a force. A scientific law is subjected to rigorous testing by a variety of experiments which are repeated many times. A valid scientific law can accurately predict natural phenomena. For example, Newton's First Law of Motion predicts that a student wearing in-line skates coasting with constant speed atop a flat, horizontal, friction-free surface would continue forever if there were no outside forces acting on the skates. If we knew the student's speed, we could predict how far the student would travel in a given amount of time. For example, if moving with a constant speed of 2 m/s for 5 sec, how far would the student move? Here we appeal to Newton's First Law, which stated algebraically is the familiar expression, distance = speed x time or d = vt.

A theory , as opposed to a scientific law, is usually not as thoroughly tested by experiments.

Either a law or a theory can sometimes explain the actual cause of the phenomenon. However, neither a law nor a theory needs to specify a cause of phenomena in nature to be considered successful. Rather to become acceptable to the community of scientists as scientific laws and theories, whether in the form of statements or algebraic expressions, the laws and theories must merely be capable of reliable predictions of natural phenomena. Scientific inquiry in the physical sciences generally proceeds not with hypothesis testing, but by developing and refining "models".

The modeling approach to learning science developed by David Hestenes and his colleagues at Arizona State University has also proved to be a very effective way to learn science¹. We will be following the modeling approach in doing experiments in this manual. 

There are basically two stages in the modeling approach: 1) model development and 2) model refinement. The first stage is generally conceptual, and the second stage refines the initial model into numerical or mathematical models. Here we will emphasize the first stage of the modeling approach to scientific inquiry, namely, model development.

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Scientific Law: A general statement based on the observed behavior of matter, to which no exceptions are known.
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scientific law

Definition

Independently and sufficiently verified description of a direct link between cause and effect of a phenomenon, deduced from experiments and/or observations. Also called laws of science, scientific laws are considered established and universally applicable (to certain class of things or phenomenon under appropriate conditions) but not necessarily definitive.
scientific law is in the Information & Knowledge Management subject.

scientific law appears in the definitions of the following terms: rule of thumb, scientific method, statistical law, Pareto principle, science and laws of science

A List of Scientific Laws
Michael Shermer on "The Scientific Method"

The scientific method-->  http://www.brandonbeltz.com/scimeth/intro1.htm

Fact vs Theory vs Law vs Hypothesis vs Proof

updated Dec 30 2013 from Reddit

 The National Academy of Sciences defining a scientific theory:

The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanationof some aspect of nature that is supported by a vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics)...One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed.

 

The American Association for the Advancement of Science weighing in:

A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact.

*updated May 16 2012 to add The scientific method

* updated May 2 2013 to add Library of Alexandria link ( which no longer works Oct 2014)

*updated February 17 2016 to add this link about gravity, theory or law?

+updated December 4 2022 to fix formatting