The self-defeating character of skepticism

An important source of doubt about our knowledge of the "external world" is the thought that all of our sensory experience could be delusive without our realizing it. For all I know, my life could be only a coherent dream in which objects and other people do not really exist. Such wholesale questioning of the deliverances of all forms of perception seems to leave us no resources for successfully justifying our belief in the existence of an objective world beyond our subjective experiences. Not all epistemologists agree with that assessment. For instance, "externalists" hold that our knowledge of the world is secure, provided that certain conditions are in fact satisfied, such as the reliability of the perceptual mechanisms giving rise to our perceptual beliefs. They do not believe it is necessary to know that our senses are reliable in order to possess knowledge about the world. This curt response to skepticism does not satisfy "internalists" who seek a way, using epistemological resources which are available to us, to justify the claim that we do in fact have reliable perceptual access to objects. Such justification might be achieved by producing a positive justification for a general "belief in objects."V Alternatively we might try to show that there is something wrong with the skeptical argument and that no such justification is necessary. In what follows I pursue the latter strategy, arguing that there is a fatal flaw in the very expression of philosophical doubt about the "external world." The feature of skepticism which I believe renders it vulnerable is the assumption that each of us has a right to be certain of his own existence as a subject of conscious experience even in the face of comprehensive doubt about our empirical beliefs. From the time of Descartes's cogito argument, philosophers have thought that the most extravagant doubts about our cognitive faculties cannot assail our assurance of our own existence. For that