English coordinators

Coordinate structures are created when two or more elements are connected by a coordinator. These structures can involve words, phrases, or clauses. For example, "apples and oranges" is a coordinate structure consisting of two noun phrases, while "She likes apples and he likes oranges" is a coordinate structure consisting of two clauses.

Unlike most phrases, coordinations are not headed. An adjective phrase, for instance, has a head adjective along with any possible dependents. In the adjective phrase very happy about it, for instance, happy is the head, very is a modifier and about it is a complement. The modifier and the complement depend on the head. In a coordination, though, the coordinated elements are equal in status, and so neither is the head. Similarly, the coordinator is only a subordinate element, not the head of the coordination.

A well-known constraint on coordinate structures is the Coordinate Structure Constraint, which states that extraction from one conjunct of a coordinate structure is not allowed. This constraint can be seen in the ungrammaticality of sentences like *What did John buy apples and? (where the asterisk indicates ungrammaticality) as opposed to the grammatical sentence What did John buy?

Coordinators are a subset of conjunctions, a broader category that also includes subordinators. While coordinators connect elements of equal syntactic importance, subordinators mark clauses as subordinate. Both coordinators and subordinators function to connect elements within a sentence, but they do so with different syntactic and semantic roles.

Coordinators differ from subordinators in that they connect elements of equal syntactic importance, while subordinators mark clauses as subordinate. Coordinators appear between the elements they connect, whereas subordinators typically appear immediately before the subordinate element, though not necessarily after the main clause. Furthermore, coordinators express relationships between the connected elements, while subordinators are often semantically empty or functional.

For example, in the sentence "She likes apples and oranges", the coordinator and connects two elements (apples and oranges) of equal importance with a cumulative sense, and in "He asked for apple or orange juice", or connects with an alternative sense. In contrast, in the sentence "She knew that he was lying", the subordinator that marks the clause "he was lying" as subordinate to the main clause "She knew" but imparts no semantic sense: "She knew he was lying" has the same meaning.

Coordinators and prepositions are both types of function words that serve to connect elements within a sentence. They share some similarities but also have important differences. Both coordinators and prepositions are used to express relationships between elements in a sentence, and they both belong to closed classes of words, meaning that their numbers are relatively fixed and new members are rarely added. Nevertheless, coordinators connect elements of equal syntactic importance, such as words, phrases, or clauses, while prepositions typically introduce phrases that function as modifiers or complements to other elements in the sentence. Coordinators appear between the elements they connect, whereas prepositions usually appear immediately before the element they introduce (e.g., a noun phrase). Coordinators often express logical relationships between the connected elements, such as addition, contrast, or alternatives (e.g., and, but, or). Prepositions, on the other hand, usually express spatial, temporal, or other semantic relationships (e.g., in, on, during).