中文摘要：

笔者认为科斯和弗里德曼两人对“假设真实性”问题认识的差异其实并没有那么大，甚至比他们自己认为的更小。弗里德曼对话的主要对象是列斯特，重点在于作为公理的基础假设是否应该是真实的。科斯对话的对象是“黑板经济学”，交易费用是科斯解释企业存在的自变量。科斯讲的假设是关于自变量的假设，不是基础假设或关于无关变量的假设。所以科斯更强调关于自变量的假设应该是真实的，而弗里德曼则更强调关于基础假设以及无关变量的假设不一定必须是真实的。厘清上述问题有助于我们更好地讨论“理性人”假设在社会学中的适用性问题。

英文摘要：

By comparing the dialogue object, the author expatiatethat there is more indifference than difference of opinion on realistic assumption between R.H.Coase and M.Friedman. Friedman debated with R A.Lester on whether assumption as postulate should be realistic. Friedman insisted that assumption as postulate or assumption on irrelevant variable need not be realistic. Coase argued with ＂blackboard econom- ics＂ and transaction cost is his independent variable to explain the firm. The realistic assumption he emphasized is not assumption as postulate or assumption on irrelevant variable, but assumption on independent variable. The above discussion may help us to understand the applicability of ＂Rational Man＂ Assumption in Sociology better .