Sentence (linguistics)

In linguistics and grammar, a sentence is a linguistic expression, such as the English example "The quick brown fox jumps over the lazy dog." In traditional grammar, it is typically defined as a string of words that expresses a complete thought, or as a unit consisting of a subject and predicate. In non-functional linguistics it is typically defined as a maximal unit of syntactic structure such as a constituent. In functional linguistics, it is defined as a unit of written texts delimited by graphological features such as upper-case letters and markers such as periods, question marks, and exclamation marks. This notion contrasts with a curve, which is delimited by phonologic features such as pitch and loudness and markers such as pauses; and with a clause, which is a sequence of words that represents some process going on throughout time. A sentence can include words grouped meaningfully to express a statement, question, exclamation, request, command, or suggestion.

A sentence is typically associated with a clause. A clause can either be a clause simplex or a clause complex. A clause simplex represents a single process going on through time. A clause complex represents a logical relation between two or more processes and is thus composed of two or more clause simplexes.

A clause (simplex) typically contains a predication structure with 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. In the examples below, the subject of the outmost clause simplex is in italics and the subject of boiling is in square brackets. There is clause embedding in the second and third examples.

There are two types of clauses: independent and non-independent/interdependent. An independent clause realises a speech act such as a statement, a question, a command or an offer. A non-independent clause does not realise any act. A non-independent clause (simplex or complex) is usually logically related to other non-independent clauses. Together, they usually constitute a single independent clause (complex). For that reason, non-independent clauses are also called interdependent. For instance, the non-independent clause because I have no friends is related to the non-independent clause I don't go out in I don't go out, because I have no friends. The whole clause complex is independent because it realises a statement. What is stated is the causal nexus between having no friend and not going out. When such a statement is acted out, the fact that the speaker doesn't go out is already established, therefore it cannot be stated. What is still open and under negotiation is the reason for that fact. The causal nexus is represented by the independent clause complex and not by the two interdependent clause simplexes.

See also copula for the consequences of the verb to be on the theory of sentence structure.

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

Sentences can also be classified based on the speech act which they perform. For instance, English sentence types can be described as follows:

The form (declarative, interrogative, imperative, or exclamative) and meaning (statement, question, command, or exclamation) of a sentence usually match, but not always. For instance, the interrogative sentence "Can you pass me the salt?" is not intended to express a question but rather to express a command. Likewise, the interrogative sentence "Can't you do anything right?" is not intended to express a question on the listener's ability, but rather to make an exclamation about the listener's lack of ability, also called a rhetorical question.