John Dryden
The fact that child found the puppy belongs to the syntactic category of sentence, that the child and the puppy are noun phrases, that found the puppy is a verb pharse, and so on, can be illustrated in a tree diagram by supplying the name of the syntactic category of each word grouping. These are often referred to as syntactic lables.
A tree diagram with syntactic category information provided is called a phrase structure tree. (it also sometimes referred to as a constituent structure tree.) this tree shows that a sentence is both a lenier string of words and hierarchical structure with phrases nested in phrases.
Three aspects of speaker's syntactic knowledge of sentence structure are disclosed in phrase structure trees :
- the linear order of the words in the sentence
- the groupings of words into particular syntactic categories
- the hierarchical structure of the syntactic categories (for example, a sentence is composed fo a noun phrase followed by a verb phrase, a verb phrase is composed of a verb that may be followed by a noun phrase, and so on )
Every sentence of English and every humman language can be represented by a phrase structure tree that explicitly reveals these properties. These trees represent the linguistic properties that are part of sperakers mental grammars.
The phrase structure tree above is correct, but it is redundant. the word child is repeated three times in the tree, puppy is repeated four times, and so on. We can streamline the tree by writing the word only once at the bottom of the diagram. Only the syntactic categories to which the word belong need to remain at the higher levels.
No information is lost in this simplified version. The syntactic category of each individual word appears immediately above that word. In this way the is shown to be a determiner, 'child a noun, and so on. The lowest categories in the tree, those immediately above the word, are called syntax categories.
The larger syntactic categories, such as verb phrase (VP), are identified as consisting of all the syntactic categories and words below that point or node in the tree. The VP in the above phrase structure tree consists of syntactic category nodes V and NP, this constituent is a noun phrase.
The phrase structure tree also states implicitly what combinations of words are not syntactic categories. For example, since there is no node above the words found and the that connects them, the two words do not constitute a syntactic category, as discussed earlier.
The phrase structure tree also shows that some syntactic categorties are composed of other syntactic categories. the sentence the child foun the puppy consists of a noun phrase, the child and a verb phrase, found the puppy. the verb phrase consists of the verb, found and the noun phrase, the puppy. The determiner the and the noun puppy together constitute a noun phrase, but individually neither is an NP.
A syntactic categories includes all the categories beneath it in the tree. For example, the S in the preceding tree is composed of an NP followed by a VP. An S is also a Det followed by an N followed by a V followed by a Det followed by an N. The 'all' is importan ; an S is not Det N V Det; that would omit the final N, which is part of the S (that is, the boy found the is not a sentence ). Every higher node is said to dominate all the nodes below it.
