ὃ γὰρ βούλεται, τοῦθ' ἕκαστος καὶ οἴεται → what he wishes to be true, each person also believes to be true | what he wishes, each person also believes
ἤισαν: Ἐπ. ἀντὶ ᾔεσαν, γ΄ πληθ. παρατ. τοῦ εἶμι (ibo).
see εἶμι.