1530s, "surmise, conjecture, supposition antecedent to knowledge," from French présupposition and directly from Medieval Latin praesuppositionem (nominative praesuppositio), noun of action from past-participle stem of Latin praesupponere, from prae "before" (see pre-) + suppositio (see suppose). Meaning "postulation as of an antecedent condition," hence "a prerequisite" is from 1570s.
1580s, "a request, demand, petition," from Latin postulātum "demand, request," properly "that which is requested," noun use of neuter past participle of postulare "to ask, demand; claim; require" (see postulate (v.)).
The sense in logic, "proposition proposed for acceptance without proof, something taken for granted," is from 1640s, from a sense in Medieval Latin. The meaning "self-evident practical proposition" is by 1751. The earlier noun in English was postulation "a petition, request" (c. 1400). Middle English also had postulate (adj.) "nominated to a bishopric or archbishopric" (mid-15c.).