O.E. þis, neuter demonstrative pronoun and adj. (masc. þes, fem. þeos), probably from a North Sea Gmc. pronoun formed by combining the base *þa- (see that) with -s, which is probably identical with O.E. se "the" (representing here "a specific thing"), but it may be O.E. seo, imperative of see (v.) "to behold." Cf. O.S. these, O.N. þessi, Du. deze, O.Fris. this, O.H.G. deser, Ger. dieser. Once fully inflected, with 10 distinct forms (see table below); the oblique cases and other genders gradually fell away by 15c. The O.E. plural was þæs (nom. and acc.), which in Northern M.E. became thas, and in Midlands and Southern England became thos. The Southern form began to be used late 13c. as the plural of that (replacing M.E. tho, from O.E. þa) and acquired an -e (apparently from the influence of M.E. adj. plurals in -e; cf. alle from all, summe from sum "some"), emerging early 14c. as modern those. About 1175 thes (probably a variant of O.E. þæs) began to be used as the plural of this, and by 1200 it had taken the form these, the final -e acquired via the same mechanism that gave one to those.
masc. Fem. Neut. Plural
Nom. þes þeos þis þas
Acc. þisne þas þis þas
Gen. þisses þisse þisses þissa
Dat. þissum þisse þissum þissum
Inst. þys þisse þys þissum
词根记忆：
pron.这(个)a.这(个);今ad.这(样)This way, sir.先生, 这边请.