Attic Pronunciation

How do you interpret that?

Σύμφωνα δὲ τὰ λοιπὰ ἑπτακαίδεκα· β γ δ ζ θ κ λ μ ν ξ π ρ σ τ φ χ ψ. σύμφωνα δὲ λέγονται, ὅτι αὐτὰ μὲν καθ᾽ ἑαυτὰ φωνὴν οὐκ ἔχει, συντασσόμενα δὲ μετὰ τῶν φωνηέντων φωνὴν ἀποτελεῖ. τούτων ἡμίφωνα μέν ἐστιν ὀκτώ· ζ ξ ψ λ μ ν ρ σ. ἡμίφωνα δὲ λέγεται, ὅτι παρ᾽ ὅσον ἧττον τῶν φωνηέντων εὔφωνα καθέστηκεν ἔν τε τοῖς μυγμοῖς καὶ σιγμοῖς. ἄφωνα δέ ἐστιν ἐννέα· β γ δ κ π τ θ φ χ. ἄφωνα δὲ λέγεται, ὅτι μᾶλλον τῶν ἄλλων ἐστὶν κακόφωνα, ὥσπερ ἄφωνον λέγομεν τὸν τραγωιδὸν τὸν κακόφωνον. τούτων ψιλὰ μέν ἐστι τρία, κ π τ, δασέα τρία, θ φ χ, μέσα δὲ τούτων τρία, β γ δ. μέσα δὲ εἴρηται, > ὅτι τῶν μὲν ψιλῶν ἐστι δασύτερα> , τῶν δὲ δασέων ψιλότερα. καὶ ἔστι τὸ μὲν β μέσον τοῦ π καὶ φ, τὸ δὲ γ μέσον τοῦ κ καὶ χ, τὸ δὲ δ μέσον τοῦ θ καὶ τ. ἀντιστοιχεῖ δὲ τὰ δασέα τοῖς ψιλοῖς, τῶι μὲν π τὸ φ, οὕτως·

How can b be τὸ μέσον of p and ? Is b δασύτερον of p and ψιλότερον of ?

English terminology:

gutterals: κ γ χ
labials: π β φ
dentals: τ δ θ

Most people nowadays conclude that δασυτερον and ψιλοτερον refer to aspiration. What the above refers to as middle, we would probably refer to as “voiced.”

So:

unvoiced: κ π τ
voiced: γ β δ
aspirated: χ φ θ

The above is from memory, so feel free to correct me.