Строй современного английского языка

TYPES OF ADVERBIAL CLAUSES
Some adverbial clauses can be easily grouped under types more or less corresponding to the types of adverbial modifiers in a simple
¹ A word of caution is necessary here. A subordinate clause introduced by the conjunction because, or when, etc., need not necessarily be an adverbial clause at all. It may, for instance, be a predicative clause, as in the sentence This was because he had just arrived. Since the subordinate clause comes immediately after the link verb be it cannot possibly be an adverbial clause but must be a predicative one.

Types of Adverbial Clauses 287
s entence, which have been considered above (p. 225 ff.). Others are more specific for the complex sentence and do not fit into "pigeonholes" arranged in accordance with the analysis of the simple sentence. Among those that will easily fit into such "pigeonholes" are clauses denoting place, those denoting time (or temporal clauses), clauses of cause, purpose, and concession, and also those of result. There are also clauses of comparison and of degree.
We may mention briefly the types of clauses which do not give much occasion for theoretical discussion, and turn our chief attention to those which do, and also to comparing subordinate clauses to the corresponding adverbial modifiers in a simple sentence, as stated above.