assume vs presume

The terms are synonomous. Both refer to accepting things as fact without proof.

The only difference is that 'assume' has better pun value, as it makes an 'ass out of u and me'

M-W.com sez that to accept without proof is a definition of presume, but it's third on the list. First is to undertake without permission, or DARE. Second definition for presume is to expect or assume with confidence... and after accept without proof is to take for granted.

Assume means primarily to take up, or use; second definition, to undertake; third, to take control of. Not until the fourth definition do you get to "to pretend to have or be." Later in the list are: to take as granted or true, and to take over someone's debts as your own.

So they're not quite the same, and neither is listed as a synonym for the other. Idiomatically, I'd use assume for, well, assumptions: "I assume dinner will be ready when we get there." I'd save presume for a more negative use: "He presumed that we'd welcome him with open arms, but we shut the door in his face."