Not necessarily...can you prove 2 + 2 = 4 without relying on any "if" propositions? How do you know that the symbol "2" means what it does? That's a proposition that you must hypothesize, so you can't write anything in your proof. How do you know that addition even works the way it does? Only because it worked that way before, but you can't express the fundamental law that makes it so. The physics of the universe can change; in dreams you are 100% "certain" of things and act on them, but these things turn out to be silly in real life. So even just to prove that 2 + 2 = 4, you have to establish a lot of conditions that themselves aren't certain or provable, so the certainty of that "truth" is not really 100%.