278c

εἰ μὲν εἰδὼς ᾗ τὸ ἀληθὲς ἔχει συνέθηκε ταῦτα,
if he composed them knowing where the truth is… this echei is impersonal requiring direct object like in modern Greek right?

Νο, ἔχει is intransitive and τὸ ἀληθὲς is its subject (nom.).