Postulation is the act of suggesting that something may be true — or the idea you put forward in that way. You are not saying you have already proved it. You set it down as a starting point so that thinking, or an argument, can go on. The matching verb is postulate. It is a formal, essay-and-science word. In everyday talk people say guess, suggest, or “maybe this is why.” Though actually, some students see post- and think “after,” as in post-war. This word is not built that way. It comes from an old Latin verb meaning to ask or to claim, not from the prefix that means after. There is also a rare church use, a formal request to put someone in a job, but the sense you will meet in learning English is the “put this forward as possibly true” one.

假定