Adjuncts

Adjuncts

adapted from a 21 April, 1997 post by JOEL MATTHEW PEARSON

If you got that impression from my definition, then I didn't do a good enough job. Relative clauses are definitely NOT complements according to common syntax parlance. They're adjuncts. The difference between complements and adjuncts is tricky to pin down, and provides a lot of fodder for heated debates in Introduction to Syntax classes. Here are a couple rules of thumb, neither of which is completely satisfactory:

Complements tend to be obligatory, while adjuncts tend to be optional. In the sentence, "John invited Mary to the masked ball", "Mary" is the complement of the verb "invited", and "to the masked ball" is an adjunct to the verb phrase "invited Mary". If you drop the complement, then the sentence becomes bad ("John invited to the masked ball"), but if you drop the adjunct, the sentence is still fine ("John invited Mary").
Heads are generally restricted to one complement apiece, whereas multiple adjuncts are allowed. Thus you can't say "John invited Mary Bill", where "invited" has two complements, but you can say "John invited Mary to the masked ball on Saturday", where "to the masked ball" and "on Saturday" are both adjuncts.

The crucial difference between complements and adjuncts, in phrase structure terms, is that when you add a complement to a head, you change that head into something else, namely a predicate phrase, whereas when you add an adjunct to a phrase, you don't change it's category or distribution. It's still a predicate phrase, just a bigger one. That is, "invited" and "invited Mary" are in a deep sense different animals, from the point of view of their distribution (i.e. "invited Mary" can combine with a subject to form a sentence, whereas "invited" cannot). But "invited Mary" and "invited Mary to the ball" are not different animals. They both count as predicate phrases.

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