1. A conditional sentence is one that assumes what may or may not be
true (in reality), and bases on it some other statement (i. e., the
supposition is assumed to be true). Bt. 600-1; Gl. 645; Gn. 1381;
H.A. 889.
2. A simple supposition implying nothing as to fulfillment, has the
indicative (or an equivalent; Bt. 602, notes) in both clauses.
(1) If a specific sequence is made in present time, then the present
indicative stands in both clauses. If in past time, a past indicative
occurs in both clauses. E. g.:
Present: εἰ τοῦτο πράττει, καλῶς ἔχει
Past: εἰ τοῦτο ἔπραττε, καλῶς εἶχε
Note 1.—The same tense need not necessarily stand in both clauses,
e. g., εἰ τοῦτο ἔπραττε, καλῶς ἔχει.
(2) A general reference if in present time, expressing a customary
or repeated action or a general truth, has ἐάν with the subjunctive
in the if-clause and in the conclusion the present indicative or some
form denoting present repetition, e. g., ἐὰν τοὺτο ποιῇ, καλῶς ἔχει.
If the supposition is in the past time, the if-clause will have the
optative with εἰ and in the conclusion will stand the imperfect
indicative or some form denoting past repetition, e. g., εἰ τοῦτο
πράττοι, καλῶς εἶχε. Bt. 608-10; Gl. 651; Gn. 1393; H.A. 890, 892-4.
3. The supposition may imply something as to the likelihood of
fulfillment.
(1) If fulfillment is likely (and such contingencies are related to
future time), then the if-clause will have ἐάν with the subjunctive
and a future indicative (or an equivalent) will stand in the conclusion.
This form is styled "future vivid." E. g., ἐὰν τοῦτο πράττῃ, καλῶς ἕξοι.
If fulfillment is less than likely ("future less vivid"), εἰ with the
optative will stand in the if-clause, the optative with ἄν (potential
optative) in the conclusion. E. g., εἰ τοῦτο πράττοι καλῶς ἄν ἔχοι.
Bt. 604-5; Gl. 650-1; Gn. 1403.
(2) A supposition contrary to fact has in the if-clause εἰ with a past
indicative; in the conclusion, a past indicative with ἄν (potential
indicative). E. g., εἰ τοῦτο ἔπραττε, καλῶς ἄν εἶχε.
Bt. 606; Gl. 649; Gn. 13197; H.A. 895.
Note 1.—For summary of conditional sentences,
see Bt. 611; Gl 645; Gn. 1387; H.A. 891.