What does Berkeley explicitly cite as the motivation behind his idealist system? How does Berkeley's idealism meet the objectives laid out by this motivation?
Berkeley hates skepticism and atheism. By his own admission, his overriding motivation in developing an idealist system was to combat these two dangerous forces.
Berkeley's hatred for atheism is self-explanatory; as a religious believer, Berkeley did not like his era's growing disbelief in God. His hatred of skepticism requires a little more explanation. Why did Berkeley care so much whether people doubted if their perceptions of reality matched the way reality really is? Why did he care if people despaired of ever knowing the true nature of things, as opposed to simply knowing their subjective impressions of these things? Why did he care if people came to believe that our senses ultimately deceive us about the true nature of reality? The short answer is: Berkeley felt that such doubts were completely contrary to common sense. No sane person really doubts that there is a world external to their own perceptions, and which roughly corresponds to those perceptions. Few people would seriously entertain a notion as absurd as, say, the possibility that an evil demon is causing all of our sensations of the world (a doubt which Descartes raises and then discards). Similarly, he thinks, it takes much philosophical training to seriously entertain the equally absurd belief that real objects are not colored, odorous, full of sound, and taste, and so on. Any person with common sense knows that the real world is just as we perceive it to be; any person with common sense trusts his or her senses.
Berkeley's hatred of skepticism probably goes beyond this mere defense of common sense, though. In all likelihood, his hatred of skepticism was very much entangled with his fear of encroaching atheism. As he has Hylas exclaim at the very opening of the first dialogue," when men of less leisure see them who are supposed to have spent their whole time in the pursuits of knowledge, professing an entire ignorance of all things, or advancing such notions as are repugnant to plan and commonly received principles, they will be tempted to entertain suspicions concerning the most important truths, which they has hitherto held sacred and unquestionable". In other words, when the learned begin to discard common sense principles, the lay people respond by discarding religious beliefs. Skepticism among the scholars leads to atheism among the masses.
Berkeley proposes to stem the tide of these two forces by positing a world system on which the only existing things are ideas and minds. God is placed squarely in the center as the ultimate causal force. By making real things into ideas (or, more specifically, into sensations), Berkeley so tightens the relationship between appearance and reality that he leaves no room for skeptical doubts. On this picture, as on the naïve common sense view, we directly experience the world as it really is, with nothing intervening to confuse or obscure our impressions. If we see a tree, we cannot doubt that it exists. And furthermore, we cannot doubt that it exists exactly as we perceive it.
On this view, of course, there are no objects external to mind which can cause our sensations. When, for instance, we have the sensation "tasting watermelon" this sensation cannot be caused by some watermelon out there in the world. However, we cannot cause these sensations ourselves, because if we did then we could control when and how they occurred. We know, therefore, that these sensations are caused by God. According to this picture, then, we cannot doubt that God exists, because God is needed in order to cause all of our sensations. God is further needed to keep all objects in existence, when no finite perceivers (i.e. people) are around to perceive them. A belief in idealism, therefore, precludes the possibility of atheism, just as it precludes the possibility of skepticism.
Why does Berkeley consider himself the defender of common sense? Do you agree with this self-assessment?
Because Berkeley's ideas are so unconventional, it is surprising that he claims that his ontology is actually a validation of common sense. The common sense view that Berkeley believes himself to be defending consists of the following interrelated ontological and epistemological claims: (1) We can trust our senses. (2) The things we see and feel are real. (3) The qualities we perceive as existing really do exist. (4) All skeptical doubt about the real existence of things is, therefore, precluded. Berkeley contrasts this common sense view with the view of philosophers, in particular the views of Descartes and Locke. The philosophical view Berkeley opposes distinguishes between subjective ideas, which exist only as the content of our consciousness, and real material things, which exist objectively in the external world and do not depend on their being apprehended by any mind in order to exist. On this view it is only the ideas and not the "real things", of which the ideas are representations, to which we have immediate access (counter to common sense claim two). Therefore, this view raises the worry of how we can know anything about the external world (counter to common sense claim four). The philosophical view also draws a distinction between primary qualities (such as size, motion, and shape) and secondary qualities (such as color, sound, taste, and smell). Primary qualities, it is said by the philosophers, really exist within the objects of perception, but secondary qualities are nothing more than ideas (counter to common sense claims one and three).
According to Berkeley's ontology, there are only two types of things existing in the world: ideas and the spirits which have them. He identifies sensible objects such as flowers, chairs, and hands, with those ideas we call "sensations". In other words, he eliminates the philosopher's distinction between the subjective impressions of sense objects and the "real existence" of those objects. The real existence of sensible objects, Berkeley claims, just is their existence as immediate objects of perception. Berkeley's identification of sensible objects with sensory impressions does seem to render trivially true those claims he regards as comprising common sense. We cannot possibly doubt the existence of something we see or touch, since its being seen or touched just is that thing's existence. There is no question, then, of whether we can trust our senses, whether the things we see and feel are real, or whether the qualities we perceive as existing really do exist. There can be no skeptical worry that we do not know the real existence of things with certainty.
Yet it seems fair to say that though Berkeley shares these four epistemic and ontological claims with a common sense view, he shares nothing else. As uncommonsensical as certain conclusions of the philosophical view are, Berkeley's own view seems to have a fundamental feature that tops them all. Berkeley is claiming, after all, that sense objects have to be perceived in order to exist. This does not sound like an assertion to which any self- respecting common man would assent. The non-philosopher is secure in his common sense conclusions, not because he rejects materially existing objects, but for the exact opposite reason - because he rejects ideas. The common sense view, far from being idealism, is simply naïve realism. The common man believes that he can trust his senses because he believes that sensation gives him direct access to the real existence of materially existing, mind-independent objects. With a direct link between our mind and the materially existing objects of sensation (with no ideas mediating) there is no room for doubting whether we can trust our senses, whether the things one sees and feels are real, whether the qualities one thinks exist do in fact exist, or whether one has certain knowledge about the real existence of things. Both the commonsensical ontology and Berkeley's ontology would render the so-called commonsensical propositions enumerated by Berkeley uninterestingly true. But since the underlying reason for these propositions are, in the two cases, so at variance, it hardly seems legitimate to claim that these two positions are at all similar.
How does Berkeley use the notion of pain to argue that all qualities are mind- dependent?
In the first dialogue, Philonous wants to show that all sensible objects are mind-dependent. He begins by trying to show that all sensible qualities are mind-dependent. In other words, he wants to prove that there is no such thing as, say, a blue ball out in the world. Blueness cannot exist outside of the mind. This, of course, sounds wrong to us. We do not think that blueness, or sweetness or roundness or whatever, depends on our mind. We think that these qualities belong to objects out in the world. We think that the ball is inherently blue and round, and would be even if there were no one around to see it.
But there is one quality that we can all agree exists only in our own minds: pain. There is no such thing as pain out in the world. No one would say that a knife contains pain, though a knife can cause pain in us if it cuts our flesh. Pain only exists when it is being perceived. We would never say that someone was in pain, but that they just could not feel it; what pain is is a feeling. Berkeley uses our intuitions about pain in order to get us to admit that all of the qualities are just like pain in this respect: they all exist only when perceived. Just as there is no such thing as pain that is not perceived, there is also no such thing as blue than is not perceived, or sweetness that is not perceived, or roundness that is not perceived.
The way Berkeley does this is to link up all the qualities with pain (or pleasure, which has the same relevant features as pain). He begins by linking heat with pain. Intense heat, he tells us, is experienced as pain. This seems undeniably true. The way that we perceive intense heat is as pain; the pain is indistinguishable from any other sensation of the heat which we might have. But if intense heat is felt as pain, then just as pain cannot exist outside of the mind, intense heat cannot exist outside of the mind. As a form of pain, intense heat only exists when it is being perceived. Since intense heat is mind- dependent, we can conclude that all degrees of heat are mind-dependent. Otherwise, we would be forced to say that as heat went up in degree, it moved from outside to inside the mind.