Simplification of written language and the change of register in the three aspects: field, tenor and mode contribute a lot to the variation of the lexicogrammatical realization in the APIA.

• 最后，本文从两个方面解释了导致美国总统就职演说的词汇语法特点发生变化的原因：即书面语言的简化及构成语域的三个因素语场、语旨和语式的变化。