reasonable和rational 都是“合理的”、“理性的”意思，使用中有时容易混淆。
reasonable
1）指行为、决定、要求、解释、期望等的合情合理，强调是“有理由的”“有道理的”；
2）指价格公平合理的；
3）指人时则表示“明智的，理智的”。
例句：
We hold that their proposal is just and reasonable.我们认为他们的建议是合情合理的。
This argument sounds reasonable, but actually it's incorrect.这种论调貌似有理, 实际上是错误的。
If your diet is reasonable, you need to have any vitamin supplements.如果你的饮食是合理的，就没必要额外补充维生素。
Your decision may be reasonable, but I still believe that he is the most qualifiedcandidate for this position.你的决定可能是合理的，但我仍然认为他是这个职位最合格的人选。
He went free because the jury decided there was a reasonable doubt about his guilt.他无罪释放，因为陪审团裁定对他犯罪的质怀是有理由的。
Our price is reasonable as compared with that in the international market.与国际市场价格相比，我们的价格是合理的。
The rent is reasonable, and moreover, the location is perfect.这房租合理，而且地点优越。
You may request her to help you. She seems like a reasonable person.你可以请求她帮你，他看来是个通情达理的人。
At last there can be a reasonable dialogue between the two governments.两国政府间最终能够进行理智的对话。
词组：
reasonable price 合理价格；价格公道reasonable distribution 合理级配reasonable time 合理期限；适当的时间
reasonable profit 合理的利润reasonable value 合理价值；合理值reasonable doubt 合理的怀疑reasonable expenses 合理费用reasonable excuse 合理解释，合理的辩解
rational
rational 侧重指思考、处理、解决问题是依照逻辑情（based on clear thought、logic andreason），是理智的、头脑清醒的、合情合理的，强调“理性”，并不是凭感觉冲动从事。
例句：All organizations and individuals must use land on a rational use.所有的组织和个人必须合理使用上使用土地。
When confronted such problems, you must resort to rational thinking and judgmentto them.遇到这样的问题，你必须进行理性的思考和判断。
As he became rational, he ought to have roused himself.既然他想通了, 就应该使自己振作起来。
In that state of mind you can't make a rational decision.在这种心态下，你无法做出理性的决定。
We must stick to the policy of making active, rational and effective use of foreigncapital.我们必须坚持积极、合理、有效地利用外资的政策。
Effective decisions making requires a rational selection of a course of action.有效的决策需要合理的选择行动方案。
词组：
rational design 合理的设计
rational choice 理性选择；理性抉择rational analysis 示构分析；示性分析rational thinking 理性思维
rational construction 结构合理；合理建构法
rational function [数]有理函数
rational number 有理数
rational behavior 理性行为
rational expectation 理性预期；合理预期
rational formula 有理公式
rational being 理性存有
rational index 有理数指数
其他近义词：
logical 合理的; 明智的；合乎逻辑的tenable 合理的；讲得通的
well-founded（报告、观念或感觉）有根据的
valid （论点、评论或观点）有根据的
level-headed 头脑冷静的；理智的sensible （行为或决定）明智的；理智的
反义词：
reasonable→unreasonable
rational→irrational
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