8.3 Constituents

We’ve started to use tree diagrams to represent how phrases are organized in our mental grammar. And we’re using the tree diagram notation to represent every single phrase as having X-bar structure. But so far I’ve just asked you to believe me about X-bar structure: I’ve told you that this is what the theory claims, but we haven’t yet talked about any evidence that our mental grammar really is organized into phrases that have X-bar structure. This unit shows some of the linguistic evidence that phrases have some reality in the mental grammar.

When we draw a tree diagram, we’re making a claim about how a sentence or phrase is organized in our mind. Every time we draw two or more branches coming together at a node, we’re making the claim that the node corresponds to a unit. In other words, all the daughters of that node behave together as a unit. Some of these nodes are at the phrase level, and some of them are at the bar-level.  The more generic term for a group of words that act together to form a unit is a constituent.

So what’s our evidence that constituents exist in our minds? Within a given sentence, how can we tell if a given string of words acts as a unit? Here again is where we rely on observing our grammaticality judgments, using a few simple tools.

Replacement Test

Here’s a simple sentence:

The students saw their friends after class.

Let’s consider the string of words their friends. Because you’ve already started to practice drawing trees, you probably have an instinct that this is a noun phrase. But if you’re going to claim that it’s a constituent, it would be nice to have some evidence for that claim. One piece of evidence is that we can replace this set of words. Take the pronoun them and replace the string of words we’re investigating:

The students saw their friends after class.

The students saw them after class.

Then we ask ourselves whether the resulting sentence is grammatical. Replacing their friends with them does indeed leave us with a grammatical sentence, which is one piece of evidence that their friends is a constituent.

Let’s test another chunk of this sentence. Let’s try the string of words after class. If we replace that set of words with the word then:

The students saw their friends after class.

The students saw their friends then.

And when we observe our grammaticality judgment, it turns out that this replacement is also grammatical. That’s some evidence that words after class behave together as a constituent in this sentence.

We can do the same thing with the string the students. Replace that string with the pronoun they:

The students saw their friends after class.

They saw their friends after class.

And observe our grammaticality judgment, and we find evidence that the students is a constituent as well.

What happens if we try to replace a string of words that isn’t a constituent?

The students saw their friends after class.

*The they friends after class.

*The did friends after class.

*The then friends after class.

*The them friends after class.

We can try lots of replacements, but when we ask ourselves whether the result is grammatical, the answer is No. There doesn’t seem to be anything that can replace the string of words students saw their. The fact that nothing can replace that string of words suggests that students saw their is not a constituent in this sentence.

At this point, you’re probably wondering how you know what you can use as a replacement. Here are some handy tips:

  • Noun Phrases can be replaced with Pronouns (it, them, they).
  • Verb Phrases can be replaced with do or do so (or did, does, doing).
  • Some Preposition Phrases (but not all) can be replaced with then or there.
  • Adjective Phrases can be replaced with something that you know to be an adjective, such as happy.

Let’s see how this replacement tool works for a verb phrase. We’ll go back to our sentence and look for the verb, saw. Let’s test this set of words: saw their friends. Since saw is the past tense of see, we’ll try replacing it with did, the past tense of do, and observe our grammaticality judgment.

The students saw their friends after class.
The students did after class.

This replacement is grammatical, so that provides us with some evidence that the set of words saw their friends is indeed a constituent.

You can use this evidence as you’re drawing trees. If you can’t quite figure out which groups of words go together into certain phrases, you can try replacing different chunks of the sentence. The parts that allow themselves to be replaced, that is, the parts that can be replaced and still leave a grammatical sentence are constituents, and those parts will be joined under one node.

You can also use this evidence when you’re trying to figure out what category a certain phrase is: If you can replace it with a pronoun, then you’ve got a noun phrase and you can look for the noun as the head. If you can replace it with do or do so, then you’ve got a verb phrase which will have a verb as its head. Then and there are a little less reliable because they sometimes replace PPs or APs, but you’ll be able to tell the difference between prepositions and adjectives because prepositions usually have complements and adjectives don’t.

Movement Test

Replacement is not the only tool we have for checking if a set of words is a constituent. Some constituents can be moved to somewhere else in the sentence without changing its meaning or its grammaticality. Preposition Phrases are especially good at being moved. Look at this sentence:

Nimra bought a top from that strange little shop.

Let’s start by targeting the last string of words by moving it to the beginning. Move the string of words then ask yourself whether the resulting sentence is grammatical.

Nimra bought a top from that strange little shop.

From that strange little shop Nimra bought a top.

Yes, it is. Standing here in isolation, the sentence might sound a little unnatural, but we can imagine a context where it would be fine, such as, “At the department store, she bought socks, at the pharmacy she bought some toothpaste, and at that strange little shop, she bought a top.” On the other hand, if we target a smaller string of words:

Nimra bought a top from that strange little shop.

*From that strange, Nimra bought a top little shop.

If we try to move that string to the beginning of the sentence, the result is a total disaster. The fact that the resulting sentence is totally ungrammatical gives us evidence that the string of words from that strange is not a constituent in this sentence.

Cleft Test

There’s a version of the movement tool that can be useful for other kinds of phrases. It’s called Clefting. A cleft is a kind of sentence that has the form:

It was ____ that …

To use the cleft test, we take the string of words that we’re investigating and put it after the words It was, then leave the remaining parts of the sentence to follow the word that. Let’s try it for the phrases we’ve already shown to be constituents.

Nimra bought a top from that strange little shop.

It was from that strange little shop that Nimra bought a top.

The students saw their friends after class.

It was their friends that the students saw after class.

It was after class that the students saw their friends.

And let’s try the cleft test on another new sentence.

Rhea’s sister baked these delicious cookies.

It was these delicious cookies that Rhea’s sister baked.

It was Rhea’s sister that baked these delicious cookies.

The cleft test shows us that the string of words these delicious cookies are a constituent, and that the words Rhea’s sister are a constituent. But look what happens if we apply the cleft test to another string of words:

Rhea’s sister baked these delicious cookies.

*It was sister baked that Rhea’s these delicious cookies.

Rhea’s sister baked these delicious cookies.

*It was these delicious that Rhea’s sister baked cookies.

Rhea’s sister baked these delicious cookies.

*It was cookies that Rhea’s sister baked these delicious.

All of these applications of the cleft test result in totally ungrammatical sentences, which gives us evidence that those underlined strings of words are not constituents in this sentence.

Answers to Questions

If a string of words is a constituent, it’s usually grammatical for it to stand alone as the answer to a question based on the sentence.

Rhea’s sister baked these delicious cookies.

What did Rhea’s sister bake? These delicious cookies.

Who baked these delicious cookies? Rhea’s sister.

The answer-to-questions test can also help us identify a verb phrase using do-replacement:

Who baked these delicious cookies? Rhea’s sister did.

Notice that in the answer, “Rhea’s sister did”, the word did automatically replaces the verb phrase baked these delicious cookies.

Again, if a string of words is not a constituent, then it is unlikely to be grammatical as the answer to a question. In fact, it’s difficult to even form the right kind of question:

What did Rhea’s sister bake cookies? *these delicious

Who of Rhea’s these delicious cookies? *sister baked

Remember that tree diagrams are a notation that linguists use to depict how phrases and sentences are organized in our mental grammar. We can’t observe mental grammar, so observing how words behave is how we make inferences about the mental grammar. These four tests are tools that we have for observing how words behave in sentences. If we discover a string of words that passes these tests, then we know that the phrase is a constituent, and therefore there should be one node that is the mother to that entire string of words in our tree diagram.

Not every constituent will pass every test, but if you’ve found that it passes two of the four tests, then you can be confident that the string is actually a constituent. When you’re drawing trees, use these tests as a check every time you draw a mother node.

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8.3 Constituents by Catherine Anderson is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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