Just a theory

24 Jul 2007

Creationism vs. Evolution is a hot topic at the moment. A common criticism (or more often: slur) against Evolution is that it is "just" a theory. It is so easy to roll your eyes at this, but it is a criticism that is not without merit if only because the word has an overloaded meaning:

  • Common usage; "in theory" as opposed to, and often different to, "in practice".
  • Scientific usage.
  • Mathematical usage; a truth derived from fact.

To any slur against Evolution on its basis as a "theory", you need to shift the person from the common usage of the word to the scientific. My problem is I've often found explaining the scientific method to a novice very hard. A slippery-slope of "weak" prepositions that seems a far cry from the popular view of science and scientific certainty.

So it was nice to find this quote today that I think sums it up quite well (via

“A theory is a meta-scientific elaboration, which is distinct from, but in harmony with, the results of observation. With the help of such a theory a group of data and independent facts can be related to one another and interpreted in one comprehensive explanation. The theory proves its validity by the measure to which it can be verified. It is constantly being tested against the facts; when it can no longer explain these facts, it shows its limits and its lack of usefulness, and it must be revised.”

This is from a 1996 writing by Pope John Paul II to the Pontifical Academy of Sciences (full text).

I like this quote because it moves a "weakness" of scientific theories -- a theory is not a truth but merely something that matches the facts -- to a strength: their explanatory power.

Explaining power and truth

Scientific theories are not truths.

Or rather, they may be true but we don't care about that so much. We only care a) if they are demonstrably not true, and more importantly b) that they are useful. There is no better example of this than Newtonian physics, which is a theory of how objects should move. Newtonian physics is demonstrably false. But the predictions (explanations) it makes for every-day sized objects are very very very close to correct. In addition, Newtonian calculations are much easier to do than the calculations of Relativistic physics (which is the rival theory). So Newtonian theory is useful.

And many other things being equal, useful trumps truth.

Well, perhaps that is a bit hyperbolic. Maybe it just trumps being false.

Anyway, and going back to the late Pontiff's quote, we must keep these two things separate:

  • the extent to which a theory matches observations made so far; and
  • accepting something as a fact.

The first of these is the domain of the scientific method. Which is a very interesting domain, and one I have had fair exposure to.

The second of these is the domain of philosophy, epistemology (study of knowledge) and belief. Which is also very interesting, but one to which I am new.

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