We’ve been working at representing how phrases and sentences are organized in the mental grammar, and to do that we’ve been using x-bar theory, which claims that every phrase in every sentence in every language of the world is organized into an x-bar structure. An x-bar structure has a head, a bar-level and a phrase level. It might, optionally, have a complement phrase as the sister to the head and daughter to the bar-level. It might, optionally, have a specifier as sister to the bar level and daughter to the phrase level.
But as you’ve been drawing trees and thinking about how sentences are organized in your mental grammar, you might have encountered some kinds of sentences that don’t seem to fit into an x-bar structure. The X-bar structures that we’ve looked at so far have left out one element. The additional level of structure that we need is called an adjunct, and here’s what it looks like. What structural relationships do you notice? The adjunct is sister to the bar-level, but here’s something we haven’t seen before: it’s also daughter to a bar-level. This is an instance of recursion. A recursive structure is a structure that contains another structure inside it that has the same type as itself. Some linguists argue that recursion is a fundamental property of all human languages and that it’s one of the things that makes human languages different from all other species’ communication systems. Try to think of some other examples of recursive structures that we’ve already seen.
So if adjunction is recursive, you’ve probably already figured out that it can happen over and over again within a single phrase. Every time we add an adjunct as sister to the bar level, we add another bar-level as its mother, to which we could add another adjunct as its sister, which adds another bar level as its mother, and so on. So an x-bar phrase can have 0 or 1 complements, and it can have either 0 or 1 specifies, but because adjuncts are recursive, it could theoretically have an infinite number of adjuncts.
We’ve got a pretty clear idea of what complements do: they complete the meaning of a head. And the specifier position is a special position for subjects. So why do we need adjuncts? Well, like complements and specifiers, adjuncts are optional: a phrase might have one or more, or it might have no adjuncts. Adjuncts often add extra information that’s not totally necessary for the meaning of the sentence, the kind of information that’s often contained in APs or PPs, like where an event happened or how it happened. Because adjuncts are optional, they can often be moved or even removed altogether without changing the grammaticality of the sentence. And many adjuncts can appear on either side of their x-bar sister, whereas in English, complements pretty much always come after their sisters and specifiers come before. Let’s look at some examples of adjunct phrases.
In this sentence, Sam bought shoes yesterday, the phrase yesterday is giving us extra information about when the buying happened, so it’s adjoined within the verb phrase headed by bought.
In this next one, Sam bought new shoes yesterday, the adjective new is giving us extra information about the noun, shoes, so it’s adjoined within the noun phrase that has shoes as its head. Notice that this AP is still in adjunct position: it’s sister to N’ and daughter to N’, but it happens to come before its sister instead of after.
And look at all the adjuncts in this one: Ted snored loudly for several hours at night. We know that the verb snore is an intransitive verb: it doesn’t take anything as its complement, so the head has no sister. But then there are three separate adjunct phrases, each of which gives us extra information about the snoring: the AP loudly is sister to V’ and daughter to another V’ node.The PP for several hours is sister to V’ and daughter of another V’ node. And the PP at night is sister to V’ and daughter to another V’ node. I’ve drawn these phrases with triangles; that’s just a shorthand that indicates that we’re not depicting the full inner structure of these phrases.
One piece of evidence that these phrases are adjuncts and not specifiers is that we can rearrange them in the sentence without changing the meaning or the grammaticality of the sentence.
Ted snored loudly for several hours at night.
Ted loudly snored at night for several hours
Ted snored for several hours at night, loudly.
If any of these phrases were complements, we wouldn’t be able to move them around, because a complement is always sister to the head, so it has to be right beside the head. But because adjunction is recursive, an adjunct always introduces another bar-level that can accommodate another adjunct.
So from now on, when you’re drawing trees, you don’t just have to decide whether each phrase goes in a complement or specifier position, but you also have to consider whether it might be an adjunct.