My apologies for the lack of posting. I've been very busy this semester. I do, however, have a moment tonight, and I have been thinking about Moore's argument for the existence of the physical world. I've been thinking about it in part because I actually read him for the first time a last month (although I was already somewhat familiar with his argument from reading Wittgenstein's On Certainty), and in part because a friend of mine recently (on my suggestion) made a remark about Berkeley in a contemporary philosophy class and was summarily dismissed with an argument almost identical to Moore's.
For those who may not be familiar, Moore's argument looks something like this:
This simple argument seems to be part of the reason why many contemporary analytic philosophers do not consider idealism a live issue (something that I intend to make it my business to change). However, it seems to me to have two enormous and equally simple defects:
Concerning the first problem: Berkeley's famous maxim is esse est percipii; "to be is to be perceived." Moore thinks he proves the existence of an external world by showing us his two hands. In fact, this proves that the external world exists in precisely the way Berkeley says it does: it's esse is percipii. To speak more clearly, if the fact that I can see two hands is conclusive evidence that the two hands exist, then Berkeley's view is correct, and perception defines reality (at least for hands). If the existence of hands was mind-independent, then even though I could see Moore's hands, they might not exist.
However, there is a bit more to Moore's argument than this, and he may be able to level an objection at Berkeley after all. The real meat of what Moore is getting at is in the third premise: Moore and Berkeley do not agree on what it means for something to be a physical object. Moore thinks that physical objects have a mind-independent reality. His real argument here, though, is that he is more certain that his hands exist as mind-independent physical objects than he is of the premises of any skeptical or idealistic argument about the physical world. Therefore, he thinks, it is more reasonable to hold to the existence of hands, and therefore physical reality, than to bow to the skeptical arguments. This, however, is where he gets into trouble with Descartes.
Descartes' argument for the existence of his soul is in fact quite similar to Moore's argument for the existence of physical substance. Moore says "I am perceiving physical objects, therefore physical objects exist;" Descartes says "I am having a subjective experience of the world, therefore my soul exists." Both Descartes and Moore are making the same mistake: they are taking a phenomenological point and drawing from them conclusions about metaphysical substances which are not objects of experience. Moore has proven that physical substance exists and Descartes has proven that mind exists, but neither have proven it in the way he seems to think he has. Moore has observed that there are perceptions, and Descartes has observed that there are subjective experiences, and these do, in my view, show that body and mind, respectively, exist in the only way possible and the only way that is meaningful for human beings. However, neither show anything about whether mind or body are metaphysical entities, and whether they are on par ontological or whether one depends on the other. Descartes simply assumes that thinking things are immaterial substances, and Moore simply assumes that perceived things are mind-independent substances, and it seems to me that these statements have approximately equal degrees of justification: namely, none whatsoever.
Thus we can see that Moore's argument cannot possibly serve as a physicalist response to Berkeley. In his defense, Moore himself did not intend his argument to respond to idealists, but to skeptics, and as an argument against skepticism it fares somewhat better. Also in Moore's defense, he wrote a separate paper, "The Refutation of Idealism," which, as the name suggests, is targeted specifically at the idealist position. This paper is sitting on my bookshelf waiting to be read. In the meantime, I hope that this post will motivate some of you to consider Berkeley's positions if not seriously enough to accept them, at least seriously enough to attempt to provide a real argument against them.