复习资料（4.10）
12、The recursiveness of phrase structure rules 短语结构规则的循环性
Significantly, these rules can generate an infinite number of sentences, and sentences with infinite length, due to their recursive properties.
Although these rules are part of the rules and regulations of the grammar, they suffice to explain how language is “creative”, and how speakers with “finite” minds have the ability to produce and understand an infinite set of sentences. That is, the recursive property captures the ability of language to generate more constituents to a sentence and enables speakers to repeat syntactic constituents within the same sentence.
由于这些短语规则的循环性，运用它们可以造出无数句子，这些句子又可以是无限长的。
这些规则虽然只是语法规则的一部分，却足以解释为什么语言具有创造性，为什么说话人的记忆力是有限的，却能表达并理解无限的句子。这就是说，循环性体现了语言中的句子能够有更多的成分，并且使说话者能够在同一个句子中重复一些句法成分。
13、X-bar theory X标杆理论
NP/VP/AP/PP all must contain one obligatory word, we call XP. This means that XP must contain X, where XP stands respectively for NP/VP/AP/PP and X stands for N/V/A/P.
The rule modified as: XP → (Specifier)X(Complement).
X 标杆理论是将各种短语结构规则高度抽象地综合成单一的X标杆规则理论。根据该理论，短语由指示语、核心词和补语组成，其中指示语和补语可有可无，但核心词却不可缺少。