Chapter 6: Syntax

6.16 Trees: Modifiers as adjuncts

When we introduced X-Bar theory, we gained the ability to represent the asymmetric relationship between heads and their complements on the one hand, and heads and their specifiers on the other hand.

At the same time, with X-Bar structure as we’ve had it so far, we lost a bit of empirical coverage that we’d been able to include in phrase structure rules: we lost a place to put modifiers:

  • AdjPs and NumPs in NPs
  • AdvPs in VPs and TPs
  • modifier PP in all other phrases

With adjuncts we expand X-Bar structure to accommodate modifiers.

The basic idea of adjuncts is that while there can only be one head in a phrase, and there can only be one phrase (because it’s the final projection of a head), a bar level is a “mid-sized phrase” or “partial phrase”, and in principle there can be many partial phrases within a larger phrase.

Let’s see how this works in practice. Consider the noun phrase (NP) in (1).

(1) [NP the early arrival of spring ]

This NP contains a modifying adjective phrase [AdjP early ]. Without that AdjP, the structure would be as shown in Figure 6.18.

Tree diagram: [NP the arrival of spring]
Figure 6.18 Tree diagram for [the arrival of spring], showing that both Specifier and Complement positions are occupied.

In this NP both the specifier and complement positions are filled, so there’s no more space for the adjective phrase [AdjP early ].

By adding additional bar levels, we can create structural “space” for modifiers. These positions are neither specifiers nor complements, instead they are adjuncts.

A constituent that is both the child and sibling of X’ is an adjunct.

Unlike specifiers and complements, adjuncts are flexible in their position: they can appear on either the left side or the right size of a phrase structure.

Figure 6.19 illustrates how an additional N’ creates space for [AdjP early ] to appear as an adjunct.

Tree diagram: [NP the early arrival of spring]
Figure 6.19 Tree diagram showing [AdjP early] as an Adjunct to N’, with the extra N’ level creating “space” for the modifier.

The same expansion of X-Bar structure gives us space within an NP to represent two PPs after the head noun, as in [NP a letter [PP from home ] [PP in the mailbox ] ]. If we run our one-replacement test, we can show that letter can be replaced by one, leaving either both PPs behind, or leaving just the second one behind. If one replaces an N-bar constituent, this means that there must be an N-bar that contains letter but not either of the PPs.

(2) a. I saw a letter from home in the mailbox, and one from the bank on the table.
b. I found that letter from home in the mailbox, and this one on the table.

The tree showing both PPs as adjuncts within NP appears in Figure 6.20.

Tree diagram for [NP the letter from home in the mailbox]
Figure 6.20 Tree diagram for [ the letter [PP from home] [PP in the mailbox], showing both PPs as Adjuncts.

Adverbs within verb phrases are also adjuncts. We’ve already seen that adverbs can go either at the beginning or end of verb phrase, as in (3a-b); we can also get more than one adverb in a verb phrase, as in (3c).

(3) a. They [VP [AdvP quickly] left the room]
b. They [VP left the room [AdvP quickly]].
c. We [VP [AdvP deliberately] left the room [AdvP slowly]].

Adverbs appearing in adjunct positions to the left and right of VP are shown in Figure 6.21.

Tree diagram: [VP deliberately left the room slowly]
Figure 6.21 Tree diagram for [VP [AdvP deliberately] left the room [AdvP slowly]], showing both adverbs as Adjuncts to V’.

All adverbs occur in adjunct positions, as do all adjective phrase inside NP. (Predicate adjectives, as in The book is long. are complements of a verb.)

PPs sometimes occur as complements, and sometimes as adjuncts—we’ve seen examples of both in this section. constituency tests like replacement with one (for N’) and do so (for V’) are very useful for figuring out if a particular PP is a complement or an adjunct.

Check your understanding

Coming soon!


If you are following the alternative path through this chapter that interleaves core concepts with tree structures, the previous section was 6.15 Trees: Sentences as TPs and the next section is 6.17 Trees: Structural ambiguity.


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Essentials of Linguistics, 2nd edition by Catherine Anderson; Bronwyn Bjorkman; Derek Denis; Julianne Doner; Margaret Grant; Nathan Sanders; and Ai Taniguchi is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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