Re: What is the difference between a theory and a law?

Date: Mon Oct 25 14:01:29 1999
Posted By: Dan Berger, MadSci Admin
Area of science: Science History
ID: 940618768.Sh

Message:

I recently read a journal article* that spurred my curiosity. The author stated, "Individuals often hold a simplistic, hierarchical view of the relationship between theories and laws whereby theories become laws depending on the availibility of supporting evidence." He added, "theories and laws are different kinds of knowledge and one can not develop or be transformed into the other" and, "theories are as legitimate a product of science as laws."

Throughout my years of undergraduate and graduate education, I have been taught this "hierarchical view" of theories and laws. As a former biology professor and current teacher of secondary education, I need to know, "What is the difference between a theory and a law?" and more importantly, CAN a theory eventually become a law based on supporting evidence? I need these questions answered in order to produce "scientifically literate" citizens, I would surley hate to continue misleading my students.

*Lederman, N.G. 1998. The state of science education: subject matter without context. The Electronic Journal of Science. 3(2).

(I was unable to locate The Electronic Journal of Science, so I linked to another presentation of the same material.)

This is a common question, and a common misconception. Unfortunately I learned it pretty much the same way you did... and didn't really have it corrected until I started digging into the philosophy of science rather recently.

The current consensus among philosophers of science seems to be this:

Laws are generalizations about what has happened, from which we can generalize about what we expect to happen. They pertain to observational data. The ability of the ancients to predict eclipses had nothing to do with whether they knew just how they happened; they had a law but not a theory.
Theories are explanations of observations (or of laws). The fact that we have a pretty good understanding of how stars explode doesn't necessarily mean we could predict the next supernova; we have a theory but not a law.

William McComus lists gravity as a modern example of a well-established law for which no really satisfying theory is available. We can use the Law of Gravity, and even correct it for the effects of relativity (General Relativity), but we don't have any consensus notion of how it functions! Is it geometry or gravitons?

Oddly enough, I searched the MadSci site and came up with a carefully- written wrong answer along the hierarchical lines you describe above. Embarassingly, several answers I summoned in my search fall into the misconceptions and traps enumerated by McComus!

We shouldn't blame our experts; as you and I have seen from our own experience, scientists may have fuzzy notions about this sort of distinction because they don't normally have to make the distinction! A working scientists doesn't tend to worry about whether the First Law of Thermodynamics is an explanation, or the Theory of Evolution a statement of observed facts. They work, she uses them, everything's fine, right? But as McComus points out, the cut-and-dried (wrong) way this is usually presented can be pretty deadly, pedagogically.

I am unable to recommend much specific for further reading, although McComus' bibliography looks to be a good place to start. You might try Richard Feynman's distinctly practical take on this problem, The Nature of Physical Law.

Dan Berger

MadSci Administrator

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