Herbert Weir Smyth, A Greek Grammar for Colleges

a. When the noun or pronoun may easily be supplied from the context. Thus, οἱ δὲ πολέμιοι, προσιόντων (τῶν Ἑλλήνων, previously mentioned), ““τέως μὲν ἡσυχίαζον” the enemy, as they were approaching, for a while remained quiet” X. A. 5.4.16, ἐρώτα_, ἔφη, ὦ Κῦρε, . . . ὡς (ἐμοῦ) τἀ_ληθῆ ἐροῦντος put your question (said he), Cyrus, on the supposition that I will speak the truth X. C. 3.1.9.

b. When the noun or pronoun may easily be supplied otherwise; here, e.g., ἀνθρώπων or πρα_γμάτων is said to be supplied grammatically. Thus, ἰόντων εἰς μάχην when (men) are going into battle X. C. 3.3.54, τοῦτον τὸν τρόπον πρα_χθέντων τῆς πόλεως γίγνεται τὰ χρήματα when (things) have happened in this way, the property belongs to the State D. 24.12; and in ὕ_οντος (Διός, 934 a) ““πολλῷ” when it was raining hard” X. H. 1.1.16. Quasi-impersonal verbs (933) thus take the genitive rather than the accusative absolute: ““οὕτως ἔχοντος” in this state of things” P. R. 381c, influenced by οὕτως ἐχόντων X. A. 3.1.40.

c. When a subordinate clause with ὅτι follows upon the participle in the passive. Thus, ““ἐσαγγελθέντων ὅτι Φοίνισσαι νῆες ἐπ᾽ αὐτοὺς πλέουσιν” it having been announced that Phoenician ships were sailing against them” T. 1.116, δηλωθέντος ὅτι ἐν ταῖς ναυσὶ τῶν Ἑλλήνων τὰ πρά_γματα ἐγένετο it having been shown that the salvation of the Greeks depended on their navy 1. 74. The plural is used when the subject of the subordinate clause is plural, or when several circumstances are mentioned.