A.T. Robertson Commentary Acts 12:9

"And he went out, and followed; and he knew not that it was true which was done by the angel, but thought he saw a vision." — Acts 12:9 (ASV)

Wist not (ουκ ηιδε). Past perfect of οιδα used as imperfect, did not know.

Followed (ηκολουθε). Imperfect active, kept on following as the angel had directed (verse 8). That it was true (οτ αληθες εστιν). Indirect assertion and so present tense retained. Note "true" (αληθες) in the sense of reality or actuality.

Which was done (το γινομενον). Present middle participle, that which was happening.

Thought he saw a vision (εδοκε οραμα βλεπειν). Imperfect active, kept on thinking, puzzled as he was. Βλεπειν is the infinitive in indirect assertion without the pronoun (he) expressed which could be either nominative in apposition with the subject as in Ro 1:22 or accusative of general reference as in Ac 5:36; 8:9 (Robertson, Grammar, pp. 1036-40). Peter had had a vision in Joppa (10:10) which Luke describes as an "ecstasy," but here is objective fact, at least Luke thought so and makes that distinction. Peter will soon know whether he is still in the cell or not as we find out that a dream is only a dream when we wake up.