Phrase structure rules generate structures. In order to turn those structures into recognizable English, we also need lexical rules that specify which words can be NP Art N NP Art N Figure 8.3 102 The Study of Language used when we rewrite constituents such as N. The first rule in the following set states that “a proper noun rewrites as Mary or George.” (It’s a very small world.)

We can rely on these rules to generate the grammatical sentences shown below as (1) to (6), but not the ungrammatical sentences shown as (7) to (12).

As a way of visualizing how the phrase structure rules form the basis of these sentences, we can draw the tree diagrams for sentences (1) and (6).