Scientific theories and laws

February 18, 2016


I've had a student ask me to clarify the difference between a scientific "law" and a "theory". This person asked, in part:

".. Is a law, in essence, something which has no detractors -> a unifying 'concept' for which scientists (at the present time) are in accordance with? Is a law a single idea by which all scientists, regardless of discipline, conform?"

" Can a theory be looked at as a 'transitory' law (i.e., a law in waiting)? In contrast to a law, is it correct to say that there can be several scientific theories about a particular phenomena whereas a law represents a single unified agreement among all scientists".

Such questions are very common. The difference between a "law" and a "theory" often confuses people. This happens, in part, because even among scientists there can be different usage of these terms. Of course, to the general public, these terms have very different meanings and connotations. I suggest that you look up the definitions of both words in any English dictionary.

As used in science, I think that it is important to realize that, in spite of the differences (see below), these terms share some things in common. both are based on tested hypotheses; both are supported by a large body of empirical data; both help unify a particular field; both are widely accepted by the vast majority (if not all) scientists within a discipline. Furthermore, both scientific laws and scientific theories could be shown to be wrong at some time if there are data to suggest so.

Presumably the acceptance of laws/theories also applies across disciplines, although most "Laws" or "Theories" are discipline specific. I can't think of law or theory that really transcends all disciplines per se; there is, as of yet, no "Unified Law (or Theory) of Everything." Most scientists aren't trained to critically analyze the pros and cons of laws or theories outside our field. For example, biologists usually aren't qualified (by training) to critique the "Theory of Relativity" or "The Atomic Theory". I don't think a physicist, chemist or engineer (by training) is qualified to discuss the details of the "Theory of Evolution" or the "Cell Theory" either.

As far as "detractors", the nature of science is to question things, nothing is (or should be) sacrosanct. But, this does not necessarily mean that just because someone questions a law (or theory) that the law/theory in question is wrong. Was Einstein a detractor of Newton when he showed that the Newtonian "Laws" of mechanics did not explain everything (wasn't that why quantum mechanics came into existence)? Just because Newtonian mechanics is "wrong" in some situations, does that mean it is useless? I don't think so!! If certain aspects of evolutionary theory (e.g., natural selection, gradualism) has "detractors" (and I mean among people who are qualified to argue about it - among biologists), does that mean natural selection (or the idea of biological evolution in general) is wrong? NO!! Scientific knowledge is strengthened by people questioning what is or has been accepted.

Here are a couple of definitions of each word.


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)

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Compare and Contrast scientific theory and law? | Yahoo Answers

Scientific theory is an unproven hypothesis (educated guess) such as the big bang theory (not the show) that has some evidence to support it but not enough to prove it.
Scientific law is a proven hypothesis that cannot change such as the laws of gravity. Last time I checked they were still working and will continue to although Hollywood would make you think different.
I hope this helps.

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