COMPLEX SENTENCES
453. The simple sentence in [§ 450] may be made complex by means of a subordinate clause used as a modifier ([§ 47]).
- The polar bear, which lives in the Arctic regions, sometimes reaches temperate latitudes.
- The polar bear sometimes reaches temperate latitudes when the ice drifts southward.
In the first example, the simple subject (bear), besides its two adjective modifiers (the and polar), takes a third, the adjective clause which lives in the Arctic regions ([§ 47]). The sentence, then, is complex: the main clause is the polar bear sometimes reaches temperate latitudes; the subordinate clause is which lives in the Arctic regions.
The second sentence is also complex. The main clause is the same as in the first (the polar bear sometimes reaches temperate latitudes). The subordinate clause is when the ice drifts southward, an adverbial modifier of the predicate verb reaches.
COMPOUND AND COMPLEX CLAUSES
454. Two or more coördinate clauses may be joined to make one compound clause.
- The polar bear, which lives in the Arctic regions and whose physical constitution is wonderfully adapted to that frigid climate, sometimes reaches temperate latitudes.
- The polar bear sometimes reaches temperate latitudes when the floes break up and when the ice drifts southward.
In the first example, the italicized words form a compound adjective clause, modifying the noun bear. It consists of two coördinate adjective clauses joined by and. These clauses are coördinate because they are of the same order or rank in the sentence ([§ 46]), each being (if taken singly) an adjective modifier of the noun.
In the second example, the predicate verb reaches is modified by a compound adverbial clause, similarly made up.