C. D. Rollins, in Solipsism, classifies solipsism into two categories, epistemological and metaphysical,1 and observes that while many philosophers have championed epistemological solipsism, no major philosopher has advocated ontological solipsism. Of epistemological solipsism he says: In some degree or style has been espoused by almost every major philosopher since Descartes. After all, is easy to believe that knowledge about what exists is empirical and that all empirical knowledge originates in inner cognitive states of persons. (Rollins, 1967, 490) Rollins indicates that for a time metaphysical solipsism was not dismissed completely-he says that was often considered implausible but incapable of being re futed2 (Rollins 1967, 488)-but that Wittgenstein's private language argument virtually dealt a death blow.3 In present essay, however, shall use considerations pertaining to Cantor's diagonal argument to suggest that private language argument is not final word on subject. When have reached this point in my argument, solipsism will still be just one theory among many; but shall then provide reasons that may increase its plausibility, even if only slightly. Metaphysical Solipsism As is well known, metaphysical solipsism has tended to be expressed by catch-phrases such as Only exist and I am whole of reality. Neither of these expressions is adequate; as Bertrand Russell, in Human Knowledge: its Scope and Limits, points out, the words have no clear meaning unless doctrine is false (Russell, 1948, 176). That aside, however-for moment, at least-the fact that metaphysical solipsism has had no major proponent is perhaps not surprising: presumably any such proponent would feel no need to record ideas for others who are considered to be illusory. Fortunately, more detailed summaries of metaphysical solipsistic position are available: Every claim concerning existence or nonexistence of anything is grounded in experience and could not possibly extend beyond it. An existential claim which seemed to reach beyond experience could have no basis or reference; would apparently be unintelligible and not strictly a claim at all. But experience is essentially immediate; in itself is never mistaken (only inferences from can be mistaken), and is had by one person only and is private to him. Hence, existential claims can never truly, and perhaps never with full intelligibility, claim more than existence of experiencing self and its states, and indeed perhaps never claim more than this as of moment of experience. (Rollins 1967, 488) It goes without saying that many philosophers have taken some or all of above ideas as a starting point for an argument, if only to criticize argument later. Descartes is obvious example of a philosopher who does this. But is generally accepted that Descartes' attempt to re-establish reality of his doubted world (by means of claiming, via ontological argument, etc., reality of God and then claiming it is impossible for him ever to deceive me [Descartes, 1941, 111]) is questionable to say least. One receives impression on reading Descartes that he is clutching, for emotional reasons (solipsism is felt to be implausible), at anything and everything that might return conviction that there is a real, exterior world. The above is not really a defense of metaphysical solipsism, of course. Are there, in fact, any generally-accepted defenses of position? Perhaps one of most telling is that there can be no absolute distinction between epistemological and metaphysical solipsism. Rollins says: One may be allowed conclusion, perhaps, that particular advocacies of knowledge solipsism do not differ from one another in having or not having resemblance to reality solipsism, but rather in degree of that resemblance. (Rollins, 1967, 490; my emphasis) This point is important, because, as mentioned above, epistemological solipsism has been almost as overwhelmingly endorsed as metaphysical solipsism has been overwhelmingly condemned. …
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