X-bar theory: We can find a common pattern with these rules: N, V, A and P in each phrase is a required lexical item for the phrase concerned.

• 我们发现这些词组都有一个共同模式：N，V，A和P分别是有关词组中所必须有的词项，也就是说，NP中必须有N，VP中必须有V，AP中必须有A，PP中必须有P。