Adjuncts are one of the five major elements of clause structure. The other four are subject (s), verb (v), object (o) and complement (c). Adjuncts (a) are some times called adverbials.
An adjunct is a phrase which is not necessary to the structure of the clause, but which adds some extra meaning to it.
In the sentenceThey waited outside for ages, the phrasesoutsideandfor agesadd extra meaning towaited. They tell us where, and for how long, the people waited. They are adjuncts:
[S]They[V]waited[A]outside[A]for ages.
[S][V]I kept[O]a copy of the letter[A]in my desk.
[S]She[A]quickly[V]realised[O]her mistake.
[A]Suddenly,[S]it[V]started to rain.
Adjuncts and complements
Adjuncts and complements are different. An adjunct is not necessary, and adds extra information. A complement is necessary in order to complete the meaning:
[S]He[V]put[O]some salt[C]in the soup.
The verbputmust have a complement sayingwheresomething is put. Without the complement (in the soup), the clause would not be complete. We cannot just sayHe put some salt.
Adjuncts and postmodifiers in noun phrases
Adjuncts are different from postmodifiers in noun phrases. An adjunct adds extra information to a clause. A postmodifier tells us more about the noun (n):
[S]They[V]’ve closed[N]that restaurant[postmodifier]on Market Street.
on Market Streetis a postmodifier. It is part of the object noun phrase. It tells us which restaurant we are talking about.
See also:
Complements
Complements and adjuncts
Noun phrases: postmodifiers