the reason到底能不能和why连用？为什么有的地方可以，有的不行？

先行词reason后接定语从句，如定语从句中缺少原因状语，则用why引导，若缺少主语或宾语，则用that或which引导，如：
This is the reason why he got angry. (缺状语)
He told us a reason which/that sounded reasonable.
(作定语从句的主语)
Can you remember the reason (that) he told us last week?
(作told的间接宾语，可省去that)

非原创