Theories and hypotheses

The differences between "theory" and "hypothesis" are important in science, but among the lay public the terms are often thought to be interchangeable. Neither of these terms is considered derogatory in science.

When I first wrote up this page, I perpetuated an error that's unfortunately all too common. Luckily a reader e-mailed me to point out my error. I'd used an explanation of theory and law in science from the online BioTech Life Science dictionary, and it's wrong, and I was wrong to use it. Where the BioTech Life Science dictionary -- and I -- went seriously wrong here is the statement that "Theories are more certain than hypotheses, but less certain than laws." This is simply not true (and I'd like to thank Andreas Johansson for e-mailing me and pointing it out).

The actual differences are more complicated, and this is an ongoing discussion within the field of philosophy of science. To try to get this as accurate as possible, I turned to a couple of online explanations of the differences, Ronald Matson's and Dan Berger's. If you'd like more explanation, I'd suggest reading both links (they're short), and here's the core part of what they have to say.

First Dan Berger:

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.

And Ronald Matson points out (quite emphatically):
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.

Now back to the term "hypothesis": a hypothesis is an idea that is generally part of or fits into a theory, and here the BioTech Life Science dictionary is on firmer ground when it notes that a hypothesis must be "an idea or proposition that is based on certain observations about the natural world." A hypothesis may be less certain than a theory or law, but it is critically important that it be based on accurate facts and a full examination of the pros and cons of the hypothesis -- otherwise you just have speculation.

That those "observations about the natural world" must be accurate, real things is taken for granted in science, and should be obvious to anyone. If your hypothesis contains inaccurate, unreal, things stated as fact, it's expected that this will be pointed out in no uncertain terms. And if you have ignored contrary facts or otherwise misrepresented what the facts are, it's expected that you will be taken to task for it. And these problems are what we see in Morgan's new book; one could say it's the thread which seems to bind all her work together into a coherent whole. Not the best legacy to leave the world, but a legacy nevertheless.