Θεωροῦντες δὲ τὴν τοῦ Πέτρου παρρησίαν καὶ Ἰωάνου, καὶ καταλαβόμενοι ὅτι ἄνθρωποι ἀγράμματοί εἰσιν καὶ ἰδιῶται, ἐθαύμαζον, ἐπεγίνωσκόν τε αὐτοὺς ὅτι σὺν τῷ Ἰησοῦ ἦσαν
When they saw the boldness of Peter and John, and discovered that they were uneducated and ordinary men, they were amazed and recognized these men had been with Jesus.
A Carm. poster claiming to have over 40 years of experience with "Greek" asserts that the Subject of the S-PN construction above is ἄνθρωποι , and that ἄνθρωποι here is indefinite, see here.
In actual fact ἄνθρωποι is part of the PN and not the S. The Subject here is αὐτοί (which refers to ὁ Πέτρος and to ὁ Ἰωάννης), the pronoun of the verb εἰσιν.
So this is how the above construction is to be understood --
αὐτοί (S) εἰσιν ἄνθρωποι ἀγράμματοί καὶ ἰδιῶται (PN)
or in other words
ὁ Πέτρος καὶ ὁ Ἰωάννης (S) εἰσιν ἄνθρωποι ἀγράμματοί καὶ ἰδιῶται (PN)
Gryllus would like us to believe the opposite:
ἄνθρωποι (S) εἰσιν ἀγράμματοί καὶ ἰδιῶται (PN)
If ἄνθρωποι is taken as the Subject then we are saying that ἄνθρωποι in general rather than αὐτοί is the subject of the verb εἰσιν and we end up with something rather crazy as follows:
"When they saw the courage of Peter and John and realized that men were unschooled and ordinary,...."
The bizarre sentence is making a generalization about men (being unlearnt and ordinary ) after having observed the courage of two specific men , namely apostles Peter and John. This is clearly false, but is what must happen if ἄνθρωποι is taken as the S of this S-PN construction. But if ἄνθρωποι is the PN then we have a proper reading -- "When they saw the courage of Peter and John and realized that they [Peter and John] were unlearned and ignorant men..."
I ask Gryllus to humbly repent of his erroneous grammar on this score. But I'm not holding my breath.