Word of the Day: Theory

There are many words which take a very different meaning in their scientific context to what they might mean in everyday use.

One such word that causes an awful lot of confusion is “theory”. As in, “theory of plate tectonics” or “theory of quantum electrodynamics“, but also as in “it’s just a theory, but…”

When people talk about having a theory in everyday language, usually they mean a hypothesis with very little evidence to back it up. A hunch, a feeling, a guess, an idea.

In science, a theory actually falls at entirely the other end of the spectrum. A theory is an explanation of the mechanism of how an observed phenomenon comes about which is strongly supported by empirical evidence.

A theory is different from a law not in the strength of it’s evidence, but in what it tells you. A theory deals with the mechanism behind a phenomenon. A law describes a phenomenon without dealing with how it comes about. If you like, a theory is an explanation, a law is a description.

This distinction causes a lot of confusion when it comes to the theory of evolution by natural selection. Evolution as a process is an observed phenomenon, not a theory. It can be seen in the lab. It can be exploited through deliberate selection by humans to create and modify domestic animal breeds. The theory part — the part that describes the mechanism — is “by natural selection.” To talk about the “theory of evolution” is to use a shorthand for the actual theory, compounding the confusion caused by not knowing the different scientific meaning of the word “theory”.

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