I knew what you meant, although "unexpressed subject" or "impersonal use" would be more accurate. However, I'm not sure how unusual the Greek actually is. In my "Homer devotional" today, Od. 7.10-11:Jonathan Robie wrote: ↑July 4th, 2020, 11:43 amI probably used the wrong word here. I tend to use the word 'antecedent' to mean 'something introduced earlier that is referred to here', which is a little sloppy. Sorry to be confusing.
Ἀλκινόῳ δʼ αὐτὴν γέρας ἔξελον, οὕνεκα πᾶσιν
Φαιήκεσσιν ἄνασσε, θεοῦ δʼ ὣς δῆμος ἄκουεν·
The previous context is talking about Nausikaa's maid, Eurymedousa, so the third person plural has no previous reference in the context. I've seen this kind of thing more than once in Homer, and I've vague memories of it in other authors as well.
The reason I commented above that the syntax was odd was not the third person plural usage, but the predicate, πρὸς αὐτὸν παραλυτικὸν αἰρόμενον ὑπὸ τεσσάρων, which obliquely (literally!) introduces the actual subject of the verb in the prepositional phrase ὑπὸ τεσσάρων.