(1)(能)推理的(having or using the ability to reason)：Man is a～animal. 人类是理性动物。Are men more～than women? 男人是不是比女人更有理性?

(2)讲(合)理的，有理智的(reasonable;sensible;not influenced by emotion)：a～explanation/plan/suggestion 一个合理的解释/计划/建议;Her behaviour isn't～. 她的行为不理智。Panic destroys～thought. 惊恐使人丧失理智。〖同〗reasonable;

(3)头脑清楚(健康)的(of sound mind)：A～man wouldn't do things like that. 一个头脑正常的人不会干那样的事。The old man was perfectly～when he made out his will. 那位老人立遗嘱时头脑很清楚。〖同〗sound;〖反〗 irrational;

【辨异】rational与reasonable都表示“讲道理，有推理能力”。 rational表示比较抽象、纯理性地推理，如：Her conclusions are always of a rational，never an emotional nature.(她的结论总是很理性的，从来不带感情色彩。)reasonable(合情理的)表示简单实际地推理，如：A reasonable supposition is one that appeals to our common sense.(所谓合理的推测就是迎合常识的推测。)