"Hypothesize" vs "postulate"

When you postulate, you're saying "let's all agree for the purposes of this discussion that (something) is true."

When you hypothesise, you're saying "Let's speculate about what would happen if (something) was true".

A hypothesis has some extra status in scientific discourse, in that scientists frequently put forward hypotheses they consider to be plausible, and perform tests to see whether they stand up to them.

Hypothesis is a theory which can after testing be accepted or rejected. A postulate is something that is assumed to be true without proof. Sometimes postulates are also called axioms.