When I first read Berkeley’s Principles and Three Dialogues some years ago, I remember being intrigued by the way Berkeley’s brand of idealism promises to dissolve the mind-body problem. Unlike the forms of dualism proposed by Descartes and Locke, there is no problem of how the mental and physical realms could interact: They don’t, because the physical realm does not exist! Yet one may wonder, as I did, whether in solving the problem of interaction we generate a new problem to take its place. For if the brain is really a family of sense impressions, it appears curious that there should be such a thing, and why damage to it should have any effect on a person’s mental functioning. In Berkeley’s system all ‘ideas’ are passive by nature, and by themselves incapable of producing anything new or causing a change in anything that already exists. In actuality ideas are mere signs which tell us what follows what; it is God who is the true cause of our ideas, the ideas themselves being simply occasions for God’s actions. That being so, couldn’t God have left the mind “floating”, without anything physical to anchor it? I used to think this was a powerful objection to Berkeley’s theory, but now I think that a Berkelian could counter it, at least if they follow Berkeley himself in accepting the existence of God. On the view I am considering, ideas may signify not only other ideas, and even other people’s thoughts and emotions, but the very principles according to which they feel and think. For someone who takes this sort of position, a brain is really a mind’s way of representing another mind. As the mind’s image, the brain would have to be organized so as to display the mind’s structure, which includes all the relationships between its various capacities and functions. Concerning the objection as to why there should be any such image of the mind, and more importantly, why damage to it results in the impairment of mental functions or even death, a theistic Berkelian can give a cogent reply. They could point out that, if there were no such image, or if damage to it did not result in the impairment of mental functions, a person’s mind would be invulnerable, and the person seemingly immortal. If the philosopher who makes the objection is both a physical realist and a theist, a theistic Berkelian can reply that for whatever reasons the physical realist may suppose God had for wanting the mind to be vulnerable, and people subject to death, a follower of Berkeley can suppose that God wanted the mind to be vulnerable, and people subject to death, for precisely the same reasons. This is because an omnipotent being such as God could easily have made the brain, as the physical realist conceives it, to be impervious to damage, either through the institution of natural laws which differ from the actual ones, or through the use of miracles (such as immediately re-growing neurons which have been damaged by a bullet to the head). So I think we can conclude that a theistic Berkelian has no special difficulty in accounting for why the brain (and hence the mind) should be vulnerable; any objection concerning the reasons God may have had for allowing damage to the brain (and hence the mind) is an objection against theism in general. Of course, the dispute over whether theism is tenable is interesting in its own right, as the existence (or otherwise) of God is perhaps the most important issue in philosophy. But that is a topic for another post.
 “Physical”, that is, in the sense of being a part of that system of ideas which includes houses and trees and stones, not in the sense that it has a material substratum or could exist unperceived.
 I use the term “physical realist” to contrast with “physicalist”. Physical realists believe that at least the physical world exists, physicalists that at most the physical world exists.
 If the theists in question are Christians, these reasons may include the Fall, God’s plan for soul-making, and doubtless many others.