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在其中不做任何成分。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。
