“众所周知,在长期中不存在固定成本”(Hall and Lieberman,1982,192),或许人们会期望一个认真的微观经济学的学生理解这句话常识的常识性。不幸的是,“长期中不存在固定成本”这一陈述无论怎样理解都是意义含混不清的,甚至可以说是个令人费解的神话。事实上,当我们将固定成本定义为“不随产量变化而变化的成本”时(Mankiw。1998,271,这是一个常用 “It is well-known that there are no fixed costs in the long run” (Hall and Lieberman, 1982, 1992), and perhaps one would expect a serious microeconomics student to understand the common sense of this sentence. Unfortunately, the statement “There is no fixed cost in the long run” is ambiguous in any sense, and can even be a puzzling myth. In fact, when we define a fixed cost as “a cost that does not vary with production volume” (Mankiw. 1998, 271, which is a commonly used