Complex sentence. Structural and functional classification.
The classification of complex sentences is usually based on the classification of subordinate clauses. Subordinate clauses are classified either on analogy with classes of words (structural classification) or on analogy with parts of the sentence (functional classification).
Structural classification. Clauses are subdivided into
- noun clauses (substantive clauses),
- adjective clauses,
- adverb clauses, etc.
But as words of the same class may perform different syntactic functions, the functional classification seems preferable. A subordinate clause can occupy any position but that of the predicate (though it may fill in the position of the predicative). There is no complete similarity between parts of the sentence and subordinate clauses. Especially this is the case with adverbial clauses.
There is a correlation between structural and functional classifications.
Accordingly to the type of clausal connection (close or loose, obligatory or optional) complex sentences may be:
The classification of complex sentences may be also based on the type of clausal connection, which may be close or loose, obligatory or optional.
Sentences with obligatory clausal connection:
1) Sentences with Subject and Predicative clauses. The subordinate clause occupies a syntactic position in the predication. It is fused, or merged with the principal clause, which is incomplete semantically and structurally: What you say is true.
2) Sentences with Object clauses. The subordinate clause is obligatory due to the obligetory valency of the predicate verb in the main clause.
3) Sentences in which there are correlative elements in both main and subordinate clauses (hardly... when; as... as; the more... the more): He was so tired, that...
Some attributive and adverbial clauses are loosely connected with the main clause and may be optional.
Composite sentences may include a number of coordinate and subordinate clauses.