All forms of skepticism that are not self-contradictory have to grant that there is some knowledge. The knowledge that they grant, and must grant, is about the immediate data of experience…Comte has given to it the name of positivism. This term suggests at once that knowledge of the sense order is positive knowledge; and also that no other knowledge is positive. It asserts knowledge of the world of sense experience and ignorance of the nature of the reality that manifests itself in that experience. What, then, shall we say of this kind of skepticism?
Taken with full seriousness, positivistic skepticism is exposed to the peculiar fate of the solipsist. The solipsist holds that nothing exists save himself and his ideas; if he seems to find things and persons outside himself, they are all really within him; responses of other human beings to his questions, tempest, and death are all alike creatures of his dream. Now, no one in his senses ever meant to believe solipsism. It is impossible to hold consistently to the view that there is nothing except one’s sensation. Further, all the arguments of Chapter II against the use of sensation as a criterion of truth may be cited in evidence here. Hence the positivistic skeptic must grant that when we talk about things and other persons than ourselves, we are talking about something other than our own sense perceptions. He must either admit or deny that he knows something about those objects. It seems peculiarly self-contradictory for positivistic skeptics to write books addressed to the intelligence of other minds, minds which are denied existence, if their own logic is sound! If, then, this sort of skeptic is to avoid solipsism and utter incoherence, he must admit that other minds exist and that he knows something about them.
(Brightman, Introduction to Philosophy, 70-71)