Herbert Weir Smyth, A Greek Grammar for Colleges

a. The appositive is nominative when a nominative precedes: ἐμέθυον: ἱκανὴ πρόφασις I was tipsy, a sufficient excuse Philemon (Com. frag. 2. 531).

b. The appositive is accusative, and states a reason, result, intention, effect, or the like: ῥί_ψει ἀπὸ πύργου, λυγρὸν ὄλεθρον will hurl thee from the battlement, a grievous death Ω 735, Ἑλένην κτάνωμεν, Μενέλεῳ λύ_πην πικρά_ν let us slay Helen and thus cause a sore grief to Menelaus E. Or. 1105, ““εὐδαιμονοίης, μισθὸν ἡδίστων λόγων” blest be thou—a return for thy most welcome tidings” E. El. 231.

N.—The appositive accusative is often cognate (1563 f.): ὁρᾷς Εὐρυσθέα_, ἄελπτον ὄψιν thou beholdest Eurystheus, an unexpected sight E. Heracl. 930.