Subordinate clauses are of three classes:
1. Substantival clauses: in which the subordinate clause plays the part of a substantive and is either the subject or the object:
δῆλον ἦν ὅτι ἐγγύς που βασιλεὺς ἦν
2. Adjectival (attributive) clauses: in which the subordinate clause plays the part of an adjective, and contains a relative whose antecedent (expressed or implied) stands in the principal clause:
λέγε δὴ τὴν ἐπιστολὴν ἣν ἔπεμψε Φίλιππος
3. Adverbial clauses: in which the subordinate clause plays the part of an adverb or adverbial expression modifying the principal clause in like manner as an adverb modifies a verb.
κραυγὴν πολλὴν ἐποίουν καλοῦντες ἀλλήλους, ὥστε καὶ τοὺς πολεμίους ἀκούειν
Accordingly all complex sentences may be classified as Substantival sentences, Adjectival sentences, and Adverbial sentences. This division is, in general, the basis of the treatment of complex sentences in this book, except when, for convenience, closely connected constructions are treated together; as in the case of (adverbial) pure final clauses and (substantival) object clauses after
Complex sentences are considered in the following order: Adverbial, Adjectival, Substantival.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].