A modifier adds optional information; a complement is required to complete the meaning.
In precise terms
Complements are arguments selected by a head and are structurally obligatory; modifiers are adjuncts, freely added or omitted. The distinction is diagnosed by obligatoriness, iterability and ordering.
An example
She put the keys on the table.
What is going on here
'On the table' is a complement of 'put', not a modifier: 'She put the keys' is incomplete. Contrast 'She read the book on the train', where the phrase is a modifier and can be dropped without damage.
Why this matters when you are learning a language
Dictionaries record which complements a verb requires, and that information is what stops you producing grammatical-looking sentences that native speakers reject. Modifiers, by contrast, are free.
Across languages
Which verbs require which complements is language-specific and rarely translates. Complements can be iterated only in limited ways, whereas modifiers stack freely in most languages.
Related terms
- Phrase and constituentIntermediate — A group of words that behaves as a single unit inside a sentence.
- ValencyAdvanced — How many participants a verb requires.
- AdjectiveBeginner — A word that describes a noun — its size, colour, quality or state.
- AdverbBeginner — A word that modifies a verb, an adjective, another adverb, or a whole clause — often saying how, when, where or to what degree.
Where to go next
- Language guides — See grammatical and lexical categories used in context.
- Terminology quiz — Test the terms on this page.