Herbert Weir Smyth, A Greek Grammar for Colleges

a. In statements of direct opposition: καὶ ταῦτά σε πολλοῦ δεῖ λεληθέναι, ἀλλὰ γὰρ οἶμαι δ̀ ἄρτι οὐκ ἔφησθα ποιεῖν, τοῦτο ποιεῖς and you are far from forgetting this, but in fact I think you are doing that which you just denied you were doing P. Charm. 166c.

N. This use is post-Homeric, rare in the drama, common in the orators and Plato. It is especially frequent in putting and setting aside an objection supposed to be raised by an opponent (hypophora). Cp. b.

b. In real and assumed objections (cp. at enim): καὶ ἀληθῆ γε ἔλεγον, ὦ Σώκρατες. ἴσως. ἀλλὰ γάρ, ὦ Εὐθύφρων, καὶ ἀλλὰ πολλὰ φῂς εἶναι ὅσια yes, and I said what was true, Socrates. Perhaps, but in fact, Euthyphron, you say that many other things too are holy P. Euth. 6d, ἀλλὰ γάρ, φήσει τις, οὐ ῥᾴδιον ἀεὶ λανθάνειν κακὸν ὄντα yes, but some one will say that it is not easy always to conceal the fact that one is wicked P. R. 365c.

c. In transitions.—(1) At the close of the discussion of an argument, where the force of ἀλλά is like that of and yet or emphatic but. Thus, ἀλλὰ γάρ, ὦ βουλή, ταῦτα μὲν ἐνθάδε οὐκ οἶδ᾽ ὅ τι δεῖ λέγειν but, Senators, I do not know why I should discuss these matters here L. 7.42, ““ἀλλὰ γὰρ ἤδη ὥρα_ ἀπιέναι” but it is already time to depart” P. A. 42a.

(2) To restrain the expression of emotion; as ἀλλ᾽ ἄναξ γάρ ἐστ᾽ ἐμός, σι_γῶ but no, I am silent for he is my king E. El. 1245.

(3) When the approach of a new actor is announced. Cp. 2817, 2818.