H. P. Grice's Identity

late L. identitās (Martianus Capella, c425), peculiarly formed from ident(i)-, for L. idem ‘same’ + -tās, -tātem: see -ty. 

Various suggestions have been offered as to the formation.

Need was evidently felt of a noun of condition or quality from idem to express the notion of ‘sameness’, side by side with those of ‘likeness’ and ‘oneness’ expressed by similitās and ūnitās: hence the form of the suffix.

But idem had no combining stem.

Some have thought that ident(i)- was taken from the L. adv. "identidem" ‘over and over again, repeatedly’, connexion with which appears to be suggested by Du Cange's explanation of identitās as ‘quævis actio repetita’.

Meyer-Lübke suggests that in the formation there was present some association between idem and id ens ‘that being’, whence "identitās" like "entitās."

But assimilation to "entitās" may have been merely to avoid the solecism of *idemitās or *idemtās.


sameness.


However originated, "ident(i)-" (either from adverb "identidem" or an assimilation of "id ens," "id ens," that being, "id entitas" "that entity") became the combining stem of idem, and the series ūnitās, ūnicus, ūnificus, ūnificāre, was paralleled by identitās, identicus, identificus, identificāre: see identic, identific, identify above.] to


OED 3rd: identity, n. Pronunciation:  Brit./ʌɪˈdɛntᵻti/ , U.S. /aɪˈdɛn(t)ədi/ Forms:  15 idemptitie, 15 ydemptyte, 15–16 identitie, 15– identity, 16 idemptity.

Etymology: < Middle French identité, ydemtité, ydemptité, ydentité (French identité) quality or condition of being the same (a1310; 1756 in sense ‘individuality, personality’, 1801 in sense ‘distinct impression of a single person or thing presented to or perceived by others’) and its etymon post-classical Latin

identitat-, identitas

quality of being the same (4th cent.), condition or fact that a person or thing is itself and not something else (8th cent. in a British source), fact of being the same (from 12th cent. in British sources), continual sameness, lack of variety, monotony (from 12th cent. in British sources; 14th cent. in a continental source) <

classical Latin idem same (see idem n.) + -tās (see -ty suffix1) [sameness],

after post-classical Latin essentitas ‘being’ (4th cent.).

The Latin word was formed to provide a translation equivalent for ancient Greek ταὐτότης (tautotes) identity.