recognise v.

early 15c., recognisen, "resume possession of land," a back-formation from recognizance, or else from Old French reconoiss-, present-participle stem of reconoistre "to know again, identify, recognize," from Latin recognoscere "acknowledge, recall to mind, know again; examine; certify," from re- "again" (see re-) + cognoscere "to get to know, recognize" (see cognizance).

With ending assimilated to verbs in -ise, -ize. The meaning "know (the object) again, recall or recover the knowledge of, perceive an identity with something formerly known or felt" is recorded from 1530s. Related: Recognized; recognizing.

word-forming element used to make verbs, Middle English -isen, from Old French -iser/-izer, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.

The variation of -ize and -ise began in Old French and Middle English, perhaps aided by a few words (such as surprise, see below) where the ending is French or Latin, not Greek. With the classical revival, English partially reverted to the correct Greek -z- spelling from late 16c. But the 1694 edition of the authoritative French Academy dictionary standardized the spellings as -s-, which influenced English.

In Britain, despite the opposition to it (at least formerly) of OED, Encyclopaedia Britannica, the Times of London, and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (such as advertise, devise, surprise). American English has always favored -ize. The spelling variation involves about 200 English verbs.