The number of conjunctions used to introduce temporal clauses is very considerable, and it seems to be growing still at the expense of nouns denoting time units, with the definite article, such as the moment, the instant, etc. Temporal clauses are used much more frequently than clauses of space.

Some adverbial clauses can be easily grouped under types more or less corresponding to the types of adverbial modifiers in a simple sentence, 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 must start the discussion of adverbial clauses by pointing out that the term "adverbial" should not be taken as an adjective derived from the noun "adverb" (which would make it a morphological term), but as a syntactical term, in the same way that it is used in the phrase "adverbial modifier" denoting a secondary part of the sentence.

A subordinate clause is said to be attributive if its function in the complex sentence is analogous to that of an attribute in a simple sentence. It differs from an attribute in so far as it characterises the thing denoted by its head word through some other action or situation in which that thing is involved. This could not, in many cases at least, be achieved within the limits of a simple sentence.

By predicative clauses we mean clauses like those in the following sentences. This was exactly what she had expected him to say and for the first time she did not go closer and squeeze his hand intimately.

The notion of a subject clause is not quite clearly defined. The idea at the bottom of the category is this: a clause which performs within a complex sentence the same function that the subject performs within a simple sentence. But in some cases this definition does not appear to be sufficient.

Above we defined a complex sentence as a sentence containing at least one subordinate clause. Any classification of complex sentences is therefore bound to be based on a classification of subordinate clauses. This will accordingly be our next task. The problem of classifying subordinate clauses is one of the vexed questions of syntactic theory. Several systems have been tried out at various times, and practically each of them has been shown to suffer from some drawback or other. Some of the classifications so far proposed have been inconsistent, that is to say, they were not based on any one firm principle of division equally applied to all clauses under consideration.

The notions of declarative, interrogative, and imperative sentence, and also that of exclamatory sentence appear to be applicable to some types of complex sentences as well. For instance, if the main clause of a complex sentence is interrogative or imperative, this implies that the complex sentence as a whole is also interrogative or imperative respectively. A few examples will suffice to illustrate our point. Why couldn't she sense now that he was outside and come out? (DREISER) The main clause Why couldn't she sense now . .. and come out? is clearly interrogative, and this is enough to make the whole complex sentence interrogative, though the subordinate clause that he was outside (an object clause) is certainly not interrogative, and should, if anything, be termed declarative. This, it may be noted in passing, is an additional proof that the clause that he was outside is a subordinate clause: its type of communication is irrelevant for the type of communication to which the sentence as a whole belongs, while the type of the clause Why couldn't she sense .. . and come out? is decisive for it.

There is much more to be said about the complex sentence than about the compound. This is due to several causes, which are, however, connected with one another.