In traditional grammar, a complex sentence is a sentence that contains an independent clause (or main clause) and at least one dependent clause. Put another way, a complex sentence is made up of a main clause with one or more dependent clauses joined to it with an appropriate conjunction or pronoun.
The complex sentence is conventionally regarded as one of the four basic sentence structures in English. The other structures are the simple sentence, the compound sentence, and the compound-complex sentence.
For an alternative definition, see Holger Diessel's remarks in Examples and Observations below.
EXAMPLES AND OBSERVATIONS
• "In the complex sentence ‘John left when his sister arrived’, the clause ‘when his sister arrived’ is a dependent clause because it is preceded by the word ‘when’, which is a subordinating conjunction. Dependent clauses are not complete sentences; they cannot stand alone as a complete sentence. For example, ‘*When his sister arrived’ cannot stand alone. Dependent clauses must be attached to independent clauses in order to form a complete sentence. In the complex sentence above, ‘John left’ is the independent clause."
—Denise E. Murray and Mary Ann Christison, What English Language Teachers Need to Know. Routledge, 2011
• Martina laughed when her mother dropped a pie upside down on the floor.
• "Because he was so small, Stuart was often hard to find around the house."
—E.B. White, Stuart Little, 1945
• "I learned a valuable lesson about cheating after I changed a mark on my report card in the third grade."—"Making the Grade"
• "If a man does not keep pace with his companions, perhaps it is because he hears a different drummer."
—Henry David Thoreau, Walden, 1854
• "He was like a cock who thought the sun had risen to hear him crow."
—George Eliot, Adam Bede, 1859
• "When my brother got his pants leg caught on the top of a high fence and hung upside down, weeping and muttering curses because his pants were newly torn and Mother would spank him for sure, no angel was with him."
—Gary Soto, A Summer Life. University Press of New England, 1990
• "The Scarecrow and the Tin Woodman stood up in a corner and kept quiet all night, although of course they could not sleep."
—L. Frank Baum, The Wonderful Wizard of Oz, 1990)
• "Although volume upon volume is written to prove slavery a very good thing, we never hear of the man who wishes to take the good of it by being a slave himself."—Abraham Lincoln, "Fragment on Slavery," July 1854
RELATIVE CLAUSES AND ADVERBIAL CLAUSES
"A complex sentence has a main clause, and one or more subordinate clauses, which come in various kinds. One kind is a relative clause, as in the [bold] parts of ‘Jack knew the kid who shot Kennedy’. They can be piled up as in ‘Jack's the guy who shot the kid who killed Kennedy’...One more common kind of subordinate clause is an adverbial clause, often stating when, how, why, or if something happened, as in the [bold] parts of these sentences: ‘If John comes, I'm leaving’, or ‘He left because he felt ill’. None of the examples just given were particularly exotic, and they could all easily have occurred in conversational speech. All were, in a technical sense, complex sentences, because they contained subordinate clauses."
—James R. Hurford, The Origins of Grammar: Language in the Light of Evolution II. Oxford University Press, 2012
POSITIONING CLAUSES IN COMPLEX SENTENCES
"Dependent clauses cannot be sentences on their own. They depend on an independent clause to support them. The independent clause in a complex sentence carries the main meaning, but either clause may come first."
—A. Robert Young and Ann O. Strauch, Nitty Gritty Grammar: Sentence Essentials for Writers. Cambridge University Press, 2006
THE NEED FOR COMPLEX SENTENCES
"Most of the sentences we use in writing or in continuous speech are complex...There is a recurrent need to expound facts or concepts in greater elaboration than the structure of the simple sentence permits."
—Walter Nash, English Usage: A Guide to First Principles. Routledge, 1986
FOUR FEATURES OF COMPLEX SENTENCES
"Complex sentences are traditionally divided into two basic types: (I) sentences including coordinate clauses, and (II) sentences including subordinate clauses. The former consist of two (or more) clauses that are functionally equivalent and symmetrical, whereas the latter consist of two (or more) clauses that constitute an asymmetrical relationship: a subordinate clause and a matrix clause do not have equal status and equal function... I suggest that prototypical subordinate clauses carry the following features: they are (I) syntactically embedded, (II) formally marked as a dependent clause, (III) semantically integrated in a superordinate clause, and (IV) part of the same processing and planning unit as the associated matrix clause."
—Holger Diessel, The Acquisition of Complex Sentences. Cambridge University Press, 2004
COMPLEX SENTENCES AND METAPHORS
"Complex sentences can offer dramatic development, extending a metaphor, as Melville's Captain Ahab reminds us: 'The path to my fixed purpose is laid on iron rails, on which my soul is grooved to run.'"
—Philip Gerard, Creative Nonfiction: Researching and Crafting Stories of Real Life. Story Press, 1996
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