Adjectives, adverbs, and substantives, of kindred meaning with the foregoing verbs, take the dative to define their meaning.
εὔνους τῷ δήμῳ
τοῖς ϝόμοις ἔνοχος
ἀδελφὰ τὰ βουλεύματα τοῖς ἔργοις
a. Some adjectives, as φίλος, ἐχθρός, may be treated as substantives and take the genitive. Some adjectives often differ slightly in meaning when they take the genitive.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].