μεγίστην δ᾽ αἰτίαν ἡγητέον ἐν ἅπαντι πράγματι καὶ πρὸς ἐπιτυχίαν καὶ τοὐναντίον τὴν τῆς πολιτείας σύστασιν: ἐκ γὰρ ταύτης ᾗπερ ἐκ πηγῆς οὐ μόνον ἀναφέρεσθαι συμβαίνει πάσας τὰς ἐπινοίας καὶ τὰς ἐπιβολὰς τῶν ἔργων, ἀλλὰ καὶ συντέλειαν λαμβάνειν.
One must study the greatest cause in all matters in respect to success and its opposite, the form of the constitution:...
The only way I can explain the first part of this sentence is by way of apposition. Another candidate might be invoking the accusative absolute for the verbal adjective, but that seems not to be allowed because of the presence of ταύτης. But I am a little hazy on how distant the subject of the absolute construction has to be from the grammatical goings on in the main clause. Mastronarde says it can't be subject, object, or anything else in the main clause. Smyth seems to just say it can't be the subject.
Any thoughts?
Thanks in advance.