Harman's hardness arguments

In "Change in View" Gilbert Harman produces arguments of the following pattern: Of two competing methods of belief revision, one is too hard; the other must therefore be the rational method. I will call arguments of this form hardness arguments. Hardness arguments are not, of course, peculiar to Harman; and considerations of this kind have recently become more popular in the philosophical literature. But Harman's hardness arguments provide an object lesson in the pitfalls of deploying such considerations.