In grammar, a modifier is an optional element in phrase structure or clause structure. A modifier is so called because it is said to modify another element in the structure, on which it is dependent. Typically the modifier can be removed without affecting the grammar of the sentence. For example, in the English sentence This is a red ball, the adjectivered is a modifier, modifying the nounball. Removal of the modifier would leave This is a ball, which is grammatically correct and equivalent in structure to the original sentence. Other terms used with a similar meaning are qualifier, attribute, and adjunct. These concepts are often distinguished from complements and arguments, which may also be considered dependent on another element, but are considered an indispensable part of the structure. For example, in His face became red, the wordred might be called a complement or argument of became, rather than a modifier or adjunct, since it cannot be omitted from the sentence.
Premodifiers and postmodifiers
Modifiers may come either before or after the modified element, depending on the type of modifier and the rules of syntax for the language in question. A modifier placed before the head is called a premodifier; one placed after the head is called a postmodifier. For example, in land mines, the word land is a premodifier of mines, whereas in the phrasemines in wartime, the phrase in wartime is a postmodifier of mines. A head may have a number of modifiers, and these may include both premodifiers and postmodifiers. For example:
In this noun phrase, man is the head, nice and tall are premodifiers, and from Canada and whom you met are postmodifiers. Notice that in English, simple adjectives are usually used as premodifiers, with occasional exceptions such as ' or the adjectives ' and ' in the phrases' and . Sometimes placement of the adjective after the noun entails a change of meaning: compare a responsible person and the person responsible, or the proper town and the town proper. It is sometimes possible for a modifier to be separated from its head by other words, as in The man came who you bumped into in the street yesterday, where the relative clausewho...yesterday is separated from the word it modifies by the word came. This type of situation is especially likely in languages with free word order.
Types
The two principal types of modifiers are adjectives, which modify nouns; and adverbs, which modify other parts of speech, particularly verbs, adjectives and other adverbs, as well as whole phrases or clauses. Another type of modifier in some languages, including English, is the noun adjunct, which is a noun modifying another noun. An example is land in the phrase land mines given above. Examples of the above types of modifiers, in English, are given below.
Sometimes it is not clear which element of the sentence a modifier is intended to modify. In many cases this is not important, but in some cases it can lead to genuine ambiguity. For example:
He painted her sitting on the step.
Here the participial phrasesitting on the step may be intended to modify her, or it may be intended to modify the verb phrasepainted her or the whole clausehe painted her, meaning in effect that it was the painter who was sitting on the step. Sometimes the element which the modifier is intended to modify does not in fact appear in the sentence, or is not in an appropriate position to be associated with that modifier. This is often considered a grammatical or stylistic error. For example:
Here whoever was "walking along the road" is not mentioned in the sentence, so the modifier has nothing to modify, except a vulture, which is clearly not the intention. Such a case is called a "dangling modifier", or more specifically, in the common case where the modifier is a participial phrase, a "dangling participle"