the reason that和the reason why这两个语法现象出现在高中英语。that和why引导的是名词从句。

　　一、前者that引导的是同位语从句,that在其中不做成分。强调与先行词同位或等同的从句叫做同位语从句。同位语从句的先行词多fact,news,ideas,thoght,reply,report,reason 等抽象名词，其关联词多为that。如：

　　The reason that he was late for school was not known.他上学迟到的原因没人知道。

　　The reason that he didn't come is clear.他没来的原因很清楚的。

　　二、后者why引导的是表示原因的原因状语从句，强调因某原因所导致的结果.。

　　That is the reason why he didn't come to your party.那就是他没来参加你的聚会的原因。

　　We don't know the reason why they didn't agree with us. 我们不知道他不同意我们的原因。