In grammar, a complement is a word, phrase, or clause that is necessary to complete the meaning of a given expression. Complements are often also arguments.
In many non-theoretical grammars, the terms subject complement and object complement are employed to denote the predicative expressions that serve to assign a property to a subject or an object: This terminology is used in grammar books: However, this use of terminology is avoided by many moderntheories of syntax, which typically view the expressions in bold as part of the clause predicate, which means they are not complements of the subject or object but rather are properties that are predicated of the subject or object. The Cambridge Grammar of the English Language assigns the term "predicative complement" to both uses and shifts the terminological distinction to the verb:
As arguments
In many modern grammars, the object argument of a verbal predicate is called a complement. In fact, this use of the term is the one that currently dominates in linguistics. A main aspect of this understanding of complements is that the subject is usually not a complement of the predicate: While it is less common to do so, one sometimes extends this reasoning to subject arguments: In those examples, the subject and object arguments are taken to be complements. In this area, the terms complement and argument thus overlap in meaning and use. Note that this practice takes a subject complement to be something very different from the subject complements of traditional grammar, which are predicative expressions, as just mentioned above.
Construed in the broadest sense, any time a given expression is somehow necessary in order to render another expression "complete", it can be characterized as a complement of that expression: Construed in the broad sense, many complements cannot be understood as arguments. The argument concept is tied to the predicate concept in a way that the complement concept is not. In linguistics, an adjunct is an optional, or structurally-dispensable, part of a sentence, clause, or phrase that, when it is removed, will not affect the remainder of the sentence except to discard from it some auxiliary information. A more detailed definition of the adjunct emphasizes its attribute as a modifying form, word, or phrase that depends on another form, word, or phrase, being an element ofclause structure with adverbial function. An adjunct is not an argument or a predicative expression, and an argument is not an adjunct. The argument-adjunct distinction is central in most theories of syntax and semantics. The terminology used to denote arguments and adjuncts can vary depending on the theory at hand. Some dependency grammars, for instance, employ the term circonstant and follow Tesnière.
