Herbert Weir Smyth, A Greek Grammar for Colleges

a. Adjectives: ὁ σοφός the wise man, τὸ δίκαιον justice.

b. Participles (with indefinite force): ὁ βουλόμενος whoever wills, the first that offers. Cp. 1124.

N. 1.—Such participial nouns appear in active, middle, and passive forms, and admit the distinctions of tense: ““οἱ ἐθελήσοντες μένειν” those who shall be willing to remain” X. H. 7.5.24.

N. 2.—Thucydides often substantivizes the neuter participle to form abstract expressions: τῆς πόλεως τὸ τι_μώμενον the dignity of the State 2. 63. Such participial nouns denote an action regulated by time and circumstance. Contrast τὸ δεδιός fear (in actual operation) 1. 36 with τὸ δέος (simply fear in the abstract).

c. Preposition and case: ““οἱ ἐπὶ τῶν πρα_γμάτων” those in power, the government” D. 18.247, ““οἱ ἐν τῇ ἡλικίᾳ” those in the prime of life” T. 6.24.

d. With the genitive, forming a noun-phrase (1299): ““τὰ τῶν στρατιωτῶν” the condition of the soldiers” X. A. 3.1.20, ““τὰ τῆς ὀργῆς” the outbursts of wrath” T. 2.60.

e. Adverbs: ““οἵ τ᾽ ἔνδον συνελαμβάνοντο καὶ οἱ ἐκτὸς κατεκόπησαν” those who were inside were arrested and those outside were cut down” X. A. 2.5.32. Similarly οἱ τότε the men of that time, οἱ ἐκεῖ the dead, οἱ πάλαι the ancients.

N.—An adverb preceded by the article may be used like an adjective: ““ὁ ὀρθῶς κυβερνήτης” the good pilot” P. R. 341c. The article is rarely omitted.

f. Infinitives: ““καλοῦσί γε ἀκολασία_ν τὸ ὑπὸ τῶν ἡδονῶν ἄρχεσθαι” they call intemperance being ruled by one's pleasures” P. Ph. 68e.

g. Any single word or clause: τὸ ὑ_μεῖς ὅταν λέγω, τὴν πόλιν λέγω when I say You, I mean the State D. 18.88, ὑπερβὰ_ς τὸ δίκα_ς ὑπεχέτω τοῦ φόνου omitting (the words) ‘let him submit to judgment for the murder’ D. 23.220.