Sentence (linguistics)

A sentence is a linguistic unit consisting of one or more words that are grammatically linked. A sentence can include words grouped meaningfully to express a statement, question, exclamation, request, command or suggestion. A sentence is a set of words that in principle tells a complete thought (although it may make little sense taken in isolation out of context); thus it may be a simple phrase, but it conveys enough meaning to imply a clause, even if it is not explicit. For example, "Two" as a sentence (in answer to the question "How many were there?") implies the clause "There were two". Typically a sentence contains a subject and predicate. A sentence can also be defined purely in orthographic terms, as a group of words starting with a capital letter and ending in a full stop. (However, this definition is useless for unwritten languages, or languages written in a system that does not employ both devices, or precise analogues thereof.) For instance, the opening of Charles Dickens's novel Bleak House begins with the following three sentences:

London. Michaelmas term lately over, and the Lord Chancellor sitting in Lincoln's Inn Hall. Implacable November weather.

The first sentence involves one word, a proper noun. The second sentence has only a non-finite verb (although using the definition given above, e.g. "Chancellor sitting in Lincoln's Inn Hall." would be a sentence by itself). The third is a single nominal group. Only an orthographic definition encompasses this variation.

In the teaching of writing skills (composition skills), students are generally required to express (rather than imply) the elements of a sentence, leading to the schoolbook definition of a sentence as one that must [explicitly] include a subject and a verb. For example, in second-language acquisition, teachers often reject one-word answers that only imply a clause, commanding the student to "give me a complete sentence", by which they mean an explicit one.

As with all language expressions, sentences might contain function and content words and contain properties such as characteristic intonation and timing patterns.

Sentences are generally characterized in most languages by the inclusion of a finite verb, e.g. "The quick brown fox jumps over the lazy dog".

Components

Clauses

A clause typically contains at least a subject noun phrase and a finite verb. Although the subject is usually a noun phrase, other kinds of phrases (such as gerund phrases) work as well, and some languages allow subjects to be omitted. There are two types of clauses: independent and subordinate (dependent). An independent clause is a complete sentence in itself, although it may not express a complete thought: for example, They did it.. A subordinate clause is not a complete sentence: for example, because I have no friends. See also copula for the consequences of the verb to be on the theory of sentence structure.

A simple complete sentence consists of a single clause. Other complete sentences consist of two or more clauses (see below).

Classification

By structure

One traditional scheme for classifying English sentences is by clause structure, the number and types of clauses in the sentence with finite verbs.

• A simple sentence consists of a single independent clause with no dependent clauses.
• A compound sentence consists of multiple independent clauses with no dependent clauses. These clauses are joined together using conjunctions, punctuation, or both.
• A complex sentence consists of one independent clause and at least one dependent clause.
• A compound–complex sentence (or complex–compound sentence) consists of multiple independent clauses, at least one of which has at least one dependent clause.

By purpose

Sentences can also be classified based on their purpose:

• A declarative sentence or declaration, the most common type, commonly makes a statement: "I have to go to work."
• An interrogative sentence or question is commonly used to request information—"Do I have to go to work?"—but sometimes not; see rhetorical question.
• An exclamatory sentence or exclamation is generally a more emphatic form of statement expressing emotion: "I have to go to work!"
• An imperative sentence or command tells someone to do something (and if done strongly may be considered both imperative and exclamatory): "Go to work." or "Go to work!"

Major and minor sentences

A major sentence is a regular sentence; it has a subject and a predicate, e.g. "I have a ball.". In this sentence, one can change the persons, e.g. "We have a ball.". However, a minor sentence is an irregular type of sentence that does not contain a main clause, e.g. "Mary!", "Precisely so.", "Next Tuesday evening after it gets dark.". Other examples of minor sentences are headings (e.g. the heading of this entry), stereotyped expressions ("Hello!"), emotional expressions ("Wow!"), proverbs, etc. These can also include nominal sentences like "The more, the merrier". These mostly omit a main verb for the sake of conciseness, but may also do so in order to intensify the meaning around the nouns.

Sentences that comprise a single word are called word sentences, and the words themselves sentence words.

Length

After a slump in interest, sentence length came to be studied in the 1980s, mostly "with respect to other syntactic phenomena".

One definition of the average sentence length of a prose passage is the ratio of the number of words to the number of sentences. The textbook Mathematical linguistics, by András Kornai, suggests that in "journalistic prose the median sentence length is above 15 words". The average length of a sentence generally serves as a measure of sentence difficulty or complexity. In general, as the average sentence length increases, the complexity of the sentences also increases.

Another definition of "sentence length" is the number of clauses in the sentence, whereas the "clause length" is the number of phones in the clause.

Research by Erik Schils and Pieter de Haan by sampling five texts showed that two adjacent sentences are more likely to have similar lengths than two non-adjacent sentences, and almost certainly have similar length when in a work of fiction. This countered the theory that "authors may aim at an alternation of long and short sentences". Sentence length, as well as word difficulty, are both factors in the readability of a sentence. However, other factors, such as the presence of conjunctions, have been said to "facilitate comprehension considerably".

See also

• Grammatical polarity
• Inflectional phrase
• Periodic sentence
• Sentence arrangement
• Sentence function
• T-unit