An Etymological Dictionary of the German Language/sich

by Friedrich Kluge

sich, pron., ‘himself, herself,’ &c., from the equiv. MidHG. sich, acc. and dat., OHG. sih, acc.; corresponding to the equiv. OLG. and Goth. sik, acc. Comp. Lat. se, Gr. ἐ, OSlov. sę, acc., ‘himself,’ &c. (sebě, dat., like Lat. sibi); Sans. sva, ‘own,’ Lat. suus, Gr. ἑός, ὅς. Hence even in Aryan there existed a reflex. pron. sve-, se-. Further details belong to grammar.