rational 与 reasonable 这两个词都有“理性的”“合理的”意思。

 (1) rational指有理性的，有思维推理能力，而不是凭感觉冲动做事。

• When people are very angry, they seldom act in a rational way.
  人们在盛怒时，很少以理性的方式行事。
• The rational side of his character has always preponderated over the emotional.
  在他的性格里，理智一向比感情占优势。

 (2) reasonable指讲道理的，合情合理的，不注重思维推理能力。

• He had always been quiet, speaking little, but always gentle, always reasonable , which was extraordinary in a young Sicilian male.
  他一向沉默寡言，但文质彬彬，通情达理——这在年轻的西西里男人中实在是异乎寻常。
• That man works very hard, so it is reasonable for him to ask for more money.
  那个人工作努力，所以他要求加薪是合情合理的。