presupposition n.

word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."

The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.

early 14c., "to assume as the basis of argument," from Old French suposer "to assume" (13c.), probably a replacement (influenced by Old French poser "put, place") of *suppondre, from Latin supponere "put or place under; to subordinate, make subject," from assimilated form of sub "under" (see sub-) + ponere "put, place" (past participle positus; see position (n.)). Meaning "to admit as possible, to believe to be true" is from 1520s.