Dionysius of Halicarnassus, On Thucydides 24
“I can summarize four the tools of Thucydides’ speech as follows: creativity in language, a variety of constructions, a harshness of order, and a swiftness of meaning. The character of his style includes density and thickness, bitterness and austerity, fierceness, and wonder and fear beyond all the emotional ranges.
This is what Thucydides is like from the character of his language in comparison to the rest. Whenever his intention and power coincide, his success is complete and divine. But whenever his force fails some and his power does not persist entirely, because of speed of his revelation, his expression becomes unclear and introduces another group of infelicities. For example, how it is right to express strange and synthetic language, how far to proceed before stopping, even though these are beautiful and necessary observations in all works, one should guard against it in all history.”
ἵνα δὲ συνελὼν εἴπω, τέτταρα μέν ἐστιν ὥσπερ ὄργανα τῆς Θουκυδίδου λέξεως· τὸ ποιητικὸν τῶν ὀνομάτων, τὸ πολυειδὲς τῶν σχημάτων, τὸ τραχὺ τῆς ἁρμονίας, τὸ τάχος τῶν σημασιῶν· χρώματα δὲ αὐτῆς τό τε στριφνὸν καὶ τὸ πυκνόν, καὶ τὸ πικρὸν καὶ τὸ αὐστηρόν, καὶ τὸ ἐμβριθὲς καὶ τὸ δεινὸν καὶ (τὸ) φοβερόν, ὑπὲρ ἅπαντα δὲ ταῦτα τὸ παθητικόν. τοιοῦτος μὲν δή τίς ἐστιν ὁ Θουκυδίδης κατὰ τὸν τῆς λέξεως χαρακτῆρα, ᾧ παρὰ τοὺς ἄλλους διήνεγκεν. ὅταν μὲν οὖν ἥ τε προαίρεσις αὐτοῦ καὶ ἡ δύναμις συνεκδράμῃ, τέλεια γίνεται κατορθώματα καὶ δαιμόνια· ὅταν δὲ ἐλλείπῃ τὸ τῆς δυνάμεως, οὐ παραμείναντος μέχρι πάντων τοῦ τόνου, διὰ τὸ τάχος τῆς ἀπαγγελίας ἀσαφής τε ἡ λέξις γίνεται καὶ ἄλλας τινὰς ἐπιφέρει κῆρας οὐκ εὐπρεπεῖς. τὸ γὰρ ἐν ᾧ δεῖ τρόπῳ τὰ ξένα καὶ πεποιημένα λέγεσθαι καὶ μέχρι πόσου προελθόντα πεπαῦσθαι, καλὰ καὶ ἀναγκαῖα θεωρήματα ἐν πᾶσιν ὄντα τοῖς ἔργοις, οὐ διὰ πάσης τῆς ἱστορίας φυλάττει