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Qiaochu_Yuan comments on Why you must maximize expected utility - Less Wrong
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No. Most humans do not maximize expected utility with respect to any utility function whatsoever because they have preferences which violate the hypotheses of the VNM theorem. For example, framing effects show that humans do not even consistently have the same preferences regarding fixed probability distributions over outcomes (but that their preferences change depending on whether the outcomes are described in terms of gains or losses).
Edit: in other words, the VNM theorem shows that "you must maximize expected utility" is equivalent to "your preferences should satisfy the hypotheses of the VNM theorem" (and not all of these hypotheses are encapsulated in the VNM axioms), and this is a statement with nontrivial content.
Axioms? (Hypotheses does seem to quite fit. One could have a hypothesis that humans had preferences that are in accord with the VNM axioms and falsify said theorem but the VNM doesn't make the hypothesis itself.)
In the nomenclature that I think is relatively standard among mathematicians, if a theorem states "if P1, P2, ... then Q" then P1, P2, ... are the hypotheses of the theorem and Q is the conclusion. One of the hypotheses of the VNM theorem, which isn't strictly speaking one of the von Neumann-Morgenstern axioms, is that you assign consistent preferences at all (that is, that the decision of whether you prefer A to B depends only on what A and B are). I'm not using "consistent" here in the same sense as the Wikipedia article does when talking about transitivity; I mean consistent over time. (Edit: Eliezer uses "incoherent"; maybe that's a better word.)
Premises.
Again, among mathematicians, I think "hypotheses" is more common. Exhibit A; Exhibit B. I would guess that "premises" is more common among philosophers...?
I usually say “assumptions”, but I'm neither a mathematician nor a philosopher. I do say “hypotheses” if for some reason I'm wearing mathematician attire.