The two words people swap by accident
In everyday speech, theory means a guess. "I have a theory about why the milk went bad." In science, the word means almost the opposite. A theory is a model that has survived a lot of attempts to break it. Evolution is a theory. Gravity is a theory. Plate tectonics is a theory. None of them are guesses. They are the most battle-tested explanations we have, with explicitly known limits.
A hypothesis, on the other hand, is a guess — but a testable one. "This drug lowers blood pressure" is a hypothesis. You can run a trial, measure, fail, succeed. "This drug is destined to heal you" is not a hypothesis — it's a vibe. It can't fail any test, because it doesn't specify one.
Why this confusion is dangerous
When someone says "evolution is just a theory," they're using everyday-theory (a guess), but the word in front of them is science-theory (battle-tested model). The two senses don't talk to each other. The argument is built on a vocabulary collision. Same trap with "climate change is just a theory."
The lens move: when you hear "just a theory," ask which sense? If it's a battle-tested model with known limits, that's the strongest thing science offers. If it's an untested guess, that's something else — and shouldn't be called a theory in a scientific argument.
Where this puts you
Most public arguments about science are vocabulary fights pretending to be evidence fights. Knowing this one distinction makes you twice as useful in any conversation about vaccines, climate, AI, evolution, or any other contested-but-actually-settled topic. Not because you'll win the argument — but because you'll see the argument's real shape.