Θηβαῖοι, like ἀλλὰ Φωκεῖς and ἀλλ᾽ ὧ τᾶν, is the answer of an imaginary objector. The Thebans were united with Philip against the Phocians in the Sacred War.
μὴ λίαν πικρὸν ἦ, “perhaps it may be too hard a saying, but . . .” This is said to be the only instance in the orators of μή introducing an independent cautious assertion. Plato is very fond of this construction, in which the idea of actual fear is never present, nor is a verb of fearing understood before μή. “We have here the original deprecatory force of ‘μή, let it not.’ In a writer like Plato this μή has become simply a suggestion put politely, and with a delicate irony” (Thompson, Attic Syntax).
τῶν ἀτοπωτάτων, neuter.
ἂν εἴη, εἰ μὴ πράξει. The fut. indic. is allowed, because optat. with ἂν is here only a softened form of the future; and πράξει is more telling, as it almost prophesies action on the part of Philip.
ἐκλαλεῖ, “blurts out,” not “blabs.”
