As has been mentioned before, the compound sentence is a polypredicative construction built on the principle of coordination(parataxis); the clauses of a compound sentence are arranged as units of syntactically equal rank, equipotently. Paradigmatically, the compound sentence is derived from two or more base sentences, joined as coordinate clauses. One of them becomes the leading clause (the “leader” clause), and the other clauses, which may or may not include the coordinative connector, occupy the dependent sentential position and may be called sequential clauses. Though the dependence between the clauses of a compound sentence is not subordinative (the sequential clause is not inserted into the position of a nominative part in the matrix sentence), the dependence is manifested positionally: by means of differences in syntactic distribution of predicative units, different distributions of the ideas expressed are achieved. Cf.: They quarreled and then they made up (again); They made up, and then they quarreled (again) (the sequence of events in time is shown as different); or, She was sick and she took some medicine (= because she was sick); She took some medicine and she became sick (= because she took the medicine) (the sequence of events in time and their causal-consequential relations are shown as different).
There has been some controversy concerning the syntactic status of the compound sentence: some linguists maintain that it is not a specific syntactic construction, but a sequence of separate sentences similar to the combination of semantically related independent sentences in speech, as in supra-sentential constructions in the text. The following arguments are used to show the arbitrariness of compound sentences: the possibility of a falling, finalizing tone between the coordinated predicative units and the possibility of using the same coordinative conjunctions for the introduction of separate sentences; cf.: They quarreled, but then they made up again. - They quarreled. But then they made up again. The fact is, there is a distinct semantico-syntactic difference between the two constructions: the closeness of connections between the events is shown by means of combining predicative units into a coordinative polypredicative sequence, while the connections between the events in a sequence of independent sentences are shown as rather loose. Besides, the subordinate clauses can also be separated in the text, being changed into specific independent sentences, but this does not challenge the status of the complex sentence as a separate syntactic unit.
Coordination, just like subordination, can be expressed either syndetically (by means of coordinative connectors) or asyndetically. Coordinative connectors, or coordinators, are divided into conjunctions proper, e.g.: and, but, or, for, either…or, neither… nor, etc., and semi-functional connectors of adverbial character, e.g.: nevertheless, besides, however, yet, thus, so, etc. Adverbial connectors, unlike pure conjunctions, can be shifted in the sequential clause (except for yet and so), e.g.: The company’s profits have fallen, but there is, however, another side to this problem. The coordinate clauses can be combined asyndetically (by the zero coordinator), e.g.: The quarrel was over, the friendship was resumed.
The intensity of cohesion between coordinate clauses can become loose, and in this case the construction is changed into a cumulative one, e.g.: I wasn’t going to leave; I’d only just arrived (cf.: I’d only just arrived and I wasn’t going to leave). Cumulative constructions have an intermediary status between the composite sentence and the sequence of independent sentences (see Unit 25).
Semantically, connections between coordinated clauses can be subdivided into two types: marked coordinative connection and unmarked coordinative connection. A marked coordination is expressed by conjunctions and adverbial connectors rendering adversative relations (but, however, yet, etc.), disjunctive relations (or, either… or, etc.),causal-consequential relations (so, for, therefore, thus, etc.), and positive and negative copulative relations of events (both... and, neither… nor). Unmarked coordination is expressed syndetically by the pure conjunction and, or asyndetically, by the zero coordinator. Relations rendered by unmarked connections are not specified in any way: they are either pure copulative relations, or enumerative relations, or broader connective meanings, which can be diagnosed by equivalent substitution with marked connections. Cf.: We started to sing and he started to sing along (unmarked coordination, copulative relations); They were sitting on the beach, the seagulls were flying above, the waves were rolling (unmarked coordination, relations of enumeration); She was sick and she took some medicine (= so she took some medicine – the relations of result or consequence).
Both unmarked and marked coordinative connections can be additionally specified when coordinators are used with an accompanying functional particle-like or adverb-like word, e.g.: and yet, and besides, but instead, but also, or else, etc.
Some compound sentences can be easily transformed into complex sentences, and in these transformations complex sentences are used as diagnostic models to expose the semantic relations between the coordinate clauses; this is of especial importance for unmarked coordinative constructions. E.g.: Water the seeds and they will grow.à If you water the seeds, they will grow;the transformation shows that the event in the first clause is the condition for that in the second; She took some medicine and she became sick.à She became sick because she took some medicine; the copulative relations between the clauses can be specified as implying that one event is the cause which generated the following event as a consequence. Coordinative connections, as such transformations show, are semantically more general than the connections in complex sentences, which are semantically more discriminatory. It must be noted, though, that the coordinative and subordinative constructions above are not equivalent and coordinative connections are not reducible to subordinative connections.
The basic type of the compound sentence, as with the complex sentence, is a two-clause construction. If more than two or more sequential clauses are combined with one leading clause, from the point of view of semantic correlation between the clauses, such constructions are divided into “open” and “closed”. “Open” constructions may be further expanded by additional clauses (as in various enumerations or descriptions), e.g.: They were sitting on the beach, the seagulls were flying above, the waves were rolling... In “closed” coordinative constructions the final part is joined on an unequal basis with the previous ones and the finalization of the chain of ideas is achieved, e.g.: He joked, he made faces, he jumped around, but the child did not smile.