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 (change the meaning of) 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 adjective red is a modifier, modifying the noun ball. 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 (the word qualify may be used in the same way as modify in this context), 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 word red might be called a complement or argument of became, rather than a modifier or adjunct, since it cannot be omitted from the sentence.
The two principal types of modifiers are adjectives (and adjectival phrases and adjectival clauses), which modify nouns; and adverbs (and adverbial phrases and adverbial clauses), which modify other parts of speech, particularly verbs, adjectives and other adverbs, as well as whole phrases or clauses. (Not all adjectives and adverbs are necessarily modifiers, however; an adjective will normally be considered a modifier when used attributively, but not when used predicatively – compare the examples with the adjective red at the start of this article.)
Another type of modifier in some languages, including English, is the noun adjunct, which is a noun modifying another noun (or occasionally another part of speech).
An example is land in the phrase land mines given above. Examples of the above types of modifiers, in English, are given below.
- It was [a nice house]. (adjective modifying a noun, in a noun phrase)
- [The swiftly flowing waters] carried it away. (adjectival phrase, in this case a participial phrase, modifying a noun in a noun phrase)
- She's [the woman with the hat]. (adjectival phrase, in this case a prepositional phrase, modifying a noun in a noun phrase)
- I saw [the man whom we met yesterday]. (adjectival clause, in this case a relative clause, modifying a noun in a noun phrase)
- His desk was in [the faculty office]. (noun adjunct modifying a noun in a noun phrase)
- [Put it gently in the drawer]. (adverb in verb phrase)
- He was [very gentle]. (adverb in adjective phrase)
- She set it down [very gently]. (adverb in adverb phrase)
- [Even more] people were there. (adverb modifying a determiner)
- It ran [right up the tree]. (adverb modifying a prepositional phrase)
- [Only the dog] was saved. (adverb modifying a noun phrase)In some cases, noun phrases or quantifiers can act as modifiers:
- [A few more] workers are needed. (quantifier modifying a determiner)
- She's [two inches taller than her sister]. (noun phrase modifying an adjective)
Ambiguous and Dangling Modifiers
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 phrase sitting on the step may be intended to modify her (meaning that the painting's subject was sitting on the step), or it may be intended to modify the verb phrase painted her or the whole clause he painted her* (or just he), 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: Walking along the road, a vulture loomed overhead. Here whoever was "walking along the road" is not mentioned in the sentence, so the modifier (walking along the road) 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 (as here) the modifier is a participial phrase, a "dangling participle".