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 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.