We think of Einstein’s theory of relativity as an exceptionally incisive scientific idea. However, Relativity pales in comparison with the awesome ramifications of Evolution—the most successful scientific theory of all time, for it explains EVERYTHING we know of life.
So, why is it called “a theory”? The answer is that the word THEORY has two levels of meaning.
(1) If I say “Mr. Trump is psychotic,” I don’t need to prove it. It may be just a “theory” to explain Trump’s erratic behavior. At this banal level “theory” means a hunch or conjecture.
(2) But if I say “Evolution is a scientific theory” I’m saying evolution has the highest and most authoritative status that science can bestow on an idea. A scientific theory must have been:
proposed as conjecture, tested and proved as hypothesis, and used by a myriad scientists to explain all relevant observations made to date (especially, those that defied explanation by any other means); it has led to new predictions which have been tested and confirmed; and it has never failed any test known to man.
Next time a creationist says “Evolution is just a theory,” tell him what the poet Alexander Pope said: “A little learning is a dangerous thing / Drink deep, or taste not the Pierian Spring.” (Or, just roll your eyes: a creationist is probably too daft to tell Alexander Pope from Pope Alexander!)