T. G. Tucker, Commentary on Thucydides: Book 8

αὐτὸς μὲν διὰ τὸ δέος, ὁ δ᾽ Ἀλκιβιάδης . . . ἐβούλετο an easily intelligible laxity of expression. αύτὸς μὲν διὰ τὸ δέος, ὁ δ᾽ Ἀλκιβιάδης διὰ τὸ βούλεσθαι κ.τ.λ would be the sequence suggested by αὐτὸς μὲν . . ., though even this of course would be a loose extension of the appositive construction (σχῆμα καθ᾽ ὅλον καὶ μέρος). There is, in fact, a confusion of two ways of speaking, viz. (1) δοκοῦσί μοι ὅ τε Τισς. καὶ ὁ Ἀλκ. τὸ αὐτὸ βουληθῆναι, ὁ μὲν Τ. διὰ τὸ δέος, ὁ δὲ Ἀ. διὰ τὸ βούλεσθαι κ.τ.λ., and (2) δοκεῖ δέ μοι ὁ Τισς. τὸ αὐτὸ βουληθῆναι, αὐτὸς μὲν διὰ τὸ δέος (αὐτὸ βουλόμενος), τοῦ δ᾽ Ἀλκ. . . . βουλομένου. . . .

καὶ ὣς v. c. 51, § 2.

ξυμβησείοντα The MS. reading ξυμβασείοντα is erroneously formed. διαβασείω is the reading in Dio C. 40, 32, but διαβησείω in Agathias, 39 D. Inf. c. 79, § 3, ναυμαχησείοντες (cf. πολεμησείω). This class of desiderative verbs is regularly formed on the sigmatic future stem (δρασείω, απαλλαξείω) The only defence of ξυμβασείω would be that correct forms in ας (γελασείω, ἐλασείω) may have prompted incorrect analogous forms, and especially where nouns like ξύμβασις, διάβασις previously existed.

ἐβούλετο κ.τ.λ. ἐβούλετο δοκεῖν belongs to all that follows, but with the subject of δοκεῖν divided: i.e. ἐβούλετο δοκεῖν (αὐτὸς) μὴ ἀδύνατος εἶναι πεῖσαι, ἀλλὰ τοὺς Ἀθηναίους μὴ ἱκανὰ διδόναι τῷ Τισς. κ.τ.λ ‘he wanted it to seem, not that he was powerless . . ., but that the Athenians, etc.’