Existence

I was reading an argument for Metaphysical Solipsism and while most of the premises were ultimately meaningless, one of them store out to me and I still am unclear about its value. “Occam's Razor This is a form of ontological parisomony which deems a competing theory a priori most likely if that theory has less ontological commitments than the other theory [4]. If two theories X and Y have the same ontological commitments, but X is ontologically committed to Z and Y is not, it would deem Y as more parsimonious than X. Thus, this argument is frameworked by the fact that metaphysical solipsism posits the fewest ontological assumptions. To promote an alternate ontology would be to assume that qualia represents a physical reality, external to the mind. It has been shown that such a fact is dubious and unjustifiable via the Trilemma, thus metaphysical solipsism ought to be deemed a priori most likely. ”Endquote Is it true that Occam’s razor seems to support Solipsism, or does it reject solipsism on the grounds that it postulates equally as many types of entities and that realism has better explanatory power? I can’t find much information on the subject of Solipsism and Ockam’s Razor so I figured I’d ask here. Thanks in advance.

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The version of Occam's Razor

The version of Occam's Razor quoted above seems to support solipsism, the view that only one's conscious experience exists, over a view which also admits the reality of the external world. After all, solipsism is committed to fewer entities than the latter view, which also countenances the existence of stars, atoms, and rollercoasters.

I'll interpret the quote that explicates Occam's Razor as holding that the following is a priori: if we have two theories, X and Y, and Y says that fewer kinds of things exist than X does, then Y is more likely to be true, on some given some body of evidence, than X. This principle does indeed indicate that we should take solipsism to be more likely to be true than realism about the external world. The problem is that the principle isn't quite right.

As it stands, the above principle says that the theory on which nothing exists is more likely to be true than any other theory, given our current evidence. No matter what you take our current evidence to be, even if you restrict our evidence to conscious experience, the theory on which nothing exists is almost certainly false. For if there were nothing, there would be no conscious experience. So, given our evidence, the theory on which nothing exists is less likely to be true than either solipsism or realism about the external world, contradicting the above version of Occam's Razor.

This is why Occam's Razor often has a clause specifying that all other theoretical virtues, aside from ontological parsimony, must be equal in order for Y to be more likely than X. By "theoretical virtues" I just mean whatever features theories can have that increase their likelihood of being true, such as explanatory power. If we were to add such a clause to the version of Occam's Razor I formulated above, it should no longer be obvious whether it supports solipsism over realism about the external world. The reason is that if realism explains more of our evidence than solipsism or explains the evidence better, this new principle will say that realism may be more likely to be true despite its positing more kinds of entities.

I leave it up to you to determine whether realism about the external world in fact has more theoretical virtues like explanatory power than solipsism does.

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