Presumer

pre·sume  (pr-zm)

v. pre·sumed, pre·sum·ing, pre·sumes

v.tr.

1. To take for granted as being true in the absence of proof to the contrary: We presumed she was innocent.

2. To constitute reasonable evidence for assuming; appear to prove: A signed hotel bill presumes occupancy of a room.

3. To venture without authority or permission; dare: He presumed to invite himself to dinner.

v.intr.

1. To act overconfidently; take liberties.

2. To take unwarranted advantage of something; go beyond the proper limits: Don't presume on their hospitality.

3. To take for granted that something is true or factual; suppose: That's the new assistant, I presume.

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[Middle English presumen, from Old French presumer, from Late Latin praesmere, from Latin, to anticipate : prae-, pre- + smere, to take; see em- in Indo-European roots.]

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pre·sumed·ly (-zmd-l) adv.

pre·sumer n.

Synonyms: presume, presuppose, postulate, posit, assume
These verbs signify to take something for granted or as being a fact. To presume is to suppose that something is reasonable or possible in the absence of proof to the contrary: "I presume you're tired after the long ride" (Edith Wharton).
Presuppose can mean to believe or suppose in advance: It is unrealistic to presuppose a sophisticated knowledge of harmony in a beginning music student.
Postulate and posit denote the assertion of the existence, reality, necessity, or truth of something as the basis for reasoning or argument: "We can see individuals, but we can't see providence; we have to postulate it" (Aldous Huxley).
To assume is to accept something as existing or being true without proof or on inconclusive grounds: "We must never assume that which is incapable of proof" (G.H. Lewes).