One way to hold this word: somebody puts a stone down on the table and says, let us all agree to start from this. Nobody has proved the stone is sound. The request is only that we accept it, so that something can be built on top. The verb is the putting-down; the noun is the stone. Everything else in an argument sits on it, which is why a bad stone brings the whole wall down.
From the word’s history
The supplied entry traces both the verb and the noun to Latin postulo, to request, with the noun from postulatum, the thing requested. The asking is still inside the modern word: you do not prove a postulate, you ask people to grant it.
來源說動詞和名詞都出自拉丁文 postulō（要求、請求），名詞來自 postulātum，也就是「被請求的那樣東西」。這層「請求」的意思到今天還在：你不是證明一個 postulate，你是請大家先答應它。
Wiktionary, "postulate" (etymology 1)
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