Proviso

(VI) To state a condition or a proviso (on condition that, provided that).

πολλὰ μὲν ἂν χρήματ᾽ ἔδωκε Φιλιστίδης ὥστ᾽ ἔχειν Ὠρεόν Philistides would have given a large sum on condition of his holding Oreus D. 18.81, ὑπῑσχνοῦντο ὥστε ἐκπλεῖν they gave their promise on the condition that they should sail out X. A. 5.6.26. On condition that is commonly expressed by ἐφ᾽ ᾧ or ἐφ᾽ ᾧτε (2279) with or without a preceding ἐπὶ τούτῳ.

ἐφ᾽ ᾧ and ἐφ᾽ ᾧτε on condition that, for the purpose of take the infinitive or (less often) the future indicative, and may be introduced, in the principal clause, by the demonstrative ἐπὶ τούτῳ. Negative μή.

αἱρεθέντες ἐφ᾽ ᾧτε συγγράψαι νόμους having been chosen for the purpose of compiling laws X. H. 2.3.11, ἔφασαν ἀποδώσειν (τοὺς νεκροὺς) ἐφ᾽ ᾧ μὴ καίειν τᾱ̀ς οἰκίᾱς the barbarians said they would surrender the dead on condition that he would not burn their houses X. A. 4.2.19, ἀφῑ́εμέν σε, ἐπὶ τούτῳ μέντοι, ἐφ᾽ ᾧτε μηκέτι . . . φιλοσοφεῖν we release you, on this condition however, that you no longer search after wisdom P. A. 29c. Future indicative: ξυνέβησαν ἐφ᾽ ᾧτε ἐξίᾱσιν ἐκ Πελοποννήσου ὑπόσπονδοι καὶ μηδέποτε ἐπιβήσονται αὐτῆς they made an agreement on condition that they should depart from the Peloponnesus under a truce and never set foot on it again T. 1.103.

a. These constructions do not occur in Homer. The future indicative is used by Herodotus and Thucydides on the analogy of relative clauses equivalent to consecutive clauses. These authors also use ἐπὶ τοῖσδε for ἐπὶ τούτῳ.