A simple explanation of the difference between laws and theories:
- 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.
even briefer:
A scientific fact is a controlled, repeatable and/or rigorously verified observation.
A scientific law is a statement of an observed regularity among facts, often expressible as a simple mathematical relationship.
A scientific theory is an integrated conceptual framework for reasoning about a class of phenomena, which is able to coordinate existing facts and laws and sometimes provide predictions of new ones.