1.可数名词 n.[C] 理由；原因
cause; why you do or say something
· I have no reason for it.
我没有理由这样做.
· Give me your reason for doing it.
告诉我你做这事的理由.
· What is the reason for your hurry?
你为什么这么匆忙?
2.不可数名词 n.[U] 理智
the power to think and make the right decision
· Only man has reason.
只有人才有理性.
· It doesn't matter what you feel,you must listen to reason.
不管你感情上怎样,你必须听从理智.
3.及物动词 vt.推理；思考
to think about something and to make the right decision
· I will reason why you are wrong.
我将思考你为什么错了.
· The ability to reason makes man different from animals.
人与动物的差别是人有思维能力.
4.不及物动词 vi.合理地思考或讨论
think or discuss logically
· I reason in this way on (about) the matter.
关于此事我从这方面思考.
与that why搭配：
the reason that后面跟原因
the reason why后面跟结果,通常前面为描述的原因