Unattainable Wish.—A wish, referring to the present or past, which cannot be realized, is expressed by a past tense of the indicative with εἴθε or with εἰ γάρ (negative μή). The imperfect refers to present time, the aorist to past time (cp. cross2304, cross2305).
εἴθ' εἶχες βελτἱ_ους φρένας
εἴθε σοι τότε συνεγενόμην
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].