来自拉丁语 ratio,思考，计算，部分，词源同 rate,reason.

1. All your arguments presuppose that he's a rational, intelligent man.

你所有论点的前提都是他是一个理性而聪明的人。

2. The arrangement presumes that both lenders and borrowers are rational.

这一协议假定借贷双方都是在神志清楚的状态下签订的。

3. He was rational and consistent in the conduct of his affairs.

他处理私事时头脑清楚，始终如一。

4. Did he come across as a sane rational person?

他看起来是一个正常而理智的人吗？

5. The alphabet might be more rational if all the vowels came first.

如果把所有的元音列在前面，字母表可能会更为合理一些。