Composite sentences are poly predicative syntactic constructions, formed by two or more predicative lines, each with a subject and a predicate of its own. Each predicative unit in a composite sentence forms a clause. A clause as a part of a composite sentence corresponds to a separate sentence. There are two principal types of composite sentences: complex and compound [6].

A composite sentence consists of two or more simple sentences joined together. The component parts of a composite sentence are called clauses. The relationship between the clauses may be that of coordination and subordination [2; 215].

In complex sentences, the clauses are united on the basis of subordinative connections. The minimal complex sentence includes two clauses: the principal one and the subordinate one. A complex sentence combines one independent clause and one or more subordinate (dependent) clauses. An independent clause contains the more important idea. E.g. After Mary came home, Bill went to have a haircut. There are three kinds of subordinate clauses – the Noun-clause, the Adjective-clause, the Adverb-clause [6].

The word “composite” is a common term for both the compound and complex sentences [12; 49].

There are three types of composite sentences in Modern English:

1. The compound sentence contains two or more independent clauses with no dependent one.
2. The complex sentence contains one dependent clause and one or more independent clauses. The latter usually tells something about the main clause and is used as a part of speech or as a part of sentence.
3. The compound-complex sentence combines the two previous types. The compound-complex sentences are those which have at least two independent clauses and at least one dependent (subordinate) clause in its structure: Blair found herself smiling at him and she took the letter he held out to her [12; 49]. There was a song in every heart; and if the heart was young the music issued at the lips (Twain).

Structurally and semantically, subordinate clauses are subordinated to principal clauses and may be joined to them by means of conjunctions, conjunctive words, asyndetically and sometimes by means of the sequence of tenses [2; 215].

In a compound sentence a clause is a part of a sentence which has a subject and a predicate of its own [3; 332].

In a compound sentence the clauses may be connected:

1. Sydentically, i.e. by means of coordinating conjunctions (and, or, else, but, etc.) or conjunctive adverbs (otherwise, however, nevertheless, yet, still, therefore, etc.).

He knew there were excuses for his father, yet he felt sick at heart (Cronin).

2. Asydentically, i.e. without a conjunction or a conjunctive adverb.

The rain fell softly, the houses was quiet (Collins) [3; 335].

A complex sentence consists of a principal clause and one or more subordinate clauses. Clauses in a complex sentences also may be linked in two ways: sydentically (More and more, she became convinced that some misfortune had overtaken Paul (Cronin)) and asydentically (I wish you had come earlier (Heym)) [3; 335].

According to their grammatical function subordinate clauses are divided into subject, predicative, attributive, object and adverbial clauses [3; 335].

For practical purposes of learning English, it is necessary and sufficient to distinguish the following kinds of subordinate clauses:

1) subject clauses which perform the function of subject and may be introduced by the conjunctions that, if, whether and such conjunctive words as who, what, which, when, why, how and others: That you may meet him at the party is quite possible. What I need now is someone to do the job.

2) predicative clauses which perform the function of predicative and may be introduced by the same conjunctions and conjunctive words as subject clauses: His only desire was that his family shouldn’t interfere with his plans. The question was why no one had heard the shot.

3) object clauses which modify verbs and adjectives as objects to them and may be introduced by the same conjunctions and conjunctive words as subject clauses: I thought (that) they were joking.

4) adverbial clauses which function as adverbial modifiers to verbs and adjectives within the principal clause and may be of the following kinds:

1. a) adverbial clauses of time which are introduced by the conjunctions when, while, as, until, till, before, after, since, as soon as, as long as and some others: When they reached the village, Jane got out of the taxi and looked about her. I won’t leave until you come.
2. b) adverbial clauses of place and direction which are introduced by the conjunction where: They stopped where the road turned to the river.
3. c) adverbial clauses of cause which are introduced by the conjunctions because, as, since and some others: He was glad to talk to her because it set her at ease.
4. d) adverbial clauses of purpose which are introduced by the conjunctions so that, that, in order that: He spoke loudly and clearly so that all could hear him.
5. e) adverbial clauses of condition which are introduced by the conjunctions if, in case, unless and some others: If we start off now, we’ll arrive there by dinner time.
6. f) adverbial clauses of concession which are introduced by the conjunctions though, although, even if, even though and wh-pronouns, ending in –ever: Although it was very late, she kept the dinner warm on the stove.
7. g) adverbial clauses of consequence which are introduced by the conjunctions that, so … that, such … that: He was so embarrassed that he could hardly understand her.
8. h) adverbial clauses of comparison which are introduced by the conjunctions than, as, as…as, not so (as)…as, as if and as though: He now took better care of his old father than he had ever done it before.