Theory Versus Hypothesis Nonscientists often use the word "theory" when they should say "hypothesis." Without getting too technical, a theory is a scientific explanation of reality that is so well tested that it is as good as a fact. The correct term for an unproven and untested explanation is "hypothesis." For example, I think it is possible that humans are the result of aliens seeding Earth with life that evolved over millions of years. I have no evidence for that idea, so it's merely a hypothesis. In conversations with friends I might call it a theory. If I blog about it, I'll play it safe and try to remember to call it a hypothesis. I've probably had more complaints about my inappropriate use of the word "theory" than any other thing I've done to anger the public, and that's a long list.