Iliad 8.140:
ἦ οὐ γιγνώσκεις ὅ τοι ἐκ Διὸς οὐχ ἕπετ ̓ ἀλκή;
“Don’t you know that no help will come your way from Zeus?”
Can anyone help me understand why there is a “ὅ” there? The Project Perseus treebank has it tagged as the neuter accusative of ὅς, so I guess it’s acting as the object of γιγνώσκω. But ὅς is a relative pronoun, so I would expect it to fit grammatically into the clause that forms the second half of the sentence as well. But it doesn’t seem to. The subject ἀλκή is feminine nominative, and the prepositional phrase ἐκ Διὸς involves a genitive.
Is ὅ being used here as some kind of particle or correlative, like English “that?” Is it neuter because it doesn’t refer to any specific noun? Accusative because that’s what γιγνώσκω wants? Could you use ὅτι here instead?