The difference between the More Vivid Future and the Less Vivid Future, like the difference between if I (
speaker sets forth a thought as prominent and distinct in his mind; and for any one or more of various reasons. Thus, he may (and generally does) regard the conclusion as more likely to be realized; but even an impossible ( cross2322 c) or dreaded result may be expressed by this form if the speaker chooses to picture the result vividly and distinctly. The More Vivid Future is thus used whenever the speaker clearly desires to be graphic, impressive, emphatic, and to anticipate a future result with the distinctness of the present.
The Less Vivid Future deals with suppositions less distinctly conceived and of less immediate concern to the speaker, mere assumed or imaginary cases. This is a favourite construction in Greek, and is often used in stating suppositions that are merely possible and often impossible; but the form of the condition itself does not imply an expectation of the speaker that the conclusion may possibly be realized. The difference between the two forms, therefore, is not an inherent difference between probable realization in the one case and possible realization in the other. The same thought may often be expressed in either form without any essential difference in meaning. The only difference is, therefore, often that of temperament, tone, or style.
a. ἐά_ν with the subjunctive and εἰ with the optative are rarely used in successive sentences. In most such cases the difference lies merely in the degree of distinctness and emphasis of the expression used; but where the speaker wishes to show that the conclusion is expected or desired, he uses ἐά_ν with the subjunctive rather than the other form. Thus, εἰ οὖν ἴδοιεν καὶ νῲ καθάπερ τοὺς πολλοὺς ἐν μεσημβρίᾳ μὴ διαλεγομένους, ἀλλὰ νυστάζοντας καὶ κηλουμένους ὑφ' αὑτῶν δι' ἀ_ργία_ν τῆς διανοία_ς, δικαίως ἂν καταγελῷεν· . . . ἐὰ_ν δ' ὁρῶσι διαλεγομένους . . ., τάχ' ἂν δοῖεν ἀγασθέντες
b. Cases of both forms in successive sentences are I 135,
c. Impossibilities may be expressed by ἐά_ν with the subjunctive. Thus, τί οὖν, ἂ_ν εἴπωσιν οἱ νόμοι; what, then,
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].