After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it "I refute it thus."
James Boswell: The Life of Samuel Johnson, LL.D. (1791)
The world is composed of matter: wind, water, and hard things like rocks that can be kicked by philosophers, whereas our awareness of the world seems to be of an altogether different character. Consciouslness, except our own, cannot be seen, heard, tasted, touched or smelled or otherwise directly shared, but can only be intimated by words, the meanings of which we learn ostensively, by reference to things that can be observed by both speaker and hearer.
The challenge of explaining consciousness has naturally attracted the attention of philosophers who seem almost as puzzled by the problem as anyone else. A solution that some philosophers have adopted is to assume that consciousness is inherent in all matter, not just brains, a theory called panpsychism.
That birds, and even bees, have conscious experience is not too difficult to believe, especially if one is aware that the nervous physiology of humans is very similar to that of other animals. But that trees, and rocks, and the flowing brook have a conscious mind seems hard for the modern mind to accept. Thus, in a recent essay in the online publication Aeon, the English philosopher Keith Frankish asserts, as have many before him, that consciousness is an illusion.
This view, however, arises from a misunderstanding of the relationship between mind and matter. The material world consists in what can, in theory, be observed by all and sundry. But consciousness is perceived only by the individual, or the brain, that is conscious. We may observe, as part of the material world, certain structures and events in a brain that correspond with reports of conscious sensations by the possessor of that brain, but the sensations of another, the color blue for example, or the scent of a rose, we cannot observe. Therefore, consciousness (as opposed to reports of consciousness) has no observable existence in the material world.
But because consciousness is absent from the observable material world, is no reason to dismiss it as an illusion or a verbal mistake, for without consciousness we could have no notion whatever about the material world.
It is the existence of the material world that is uncertain, not consciousness, which is directly experienced. Consciousness is unquestionably real, whereas the material world is merely inferred from conscious experience. Thus, Berkeleyan idealism that dismisses, or at least disregards, the existence of a material world altogether, is the most rational way of looking at things.
But it is the solipsistic implication of idealism, the idea that nothing exists other than the observer's own mind, that evokes resistance to the idealist view. But since awareness of the material world or of other minds consists in nothing other than a collection of conscious percepts, it is of no logical significance whether one believes in a material world and other minds or not. Either way, one's conscious experience of the world will be exactly the same.
As a practical matter, the existence of an external world is a useful assumption since language is based upon that assumption, and to speak without accepting that assumption entails some convolution in expression.
Moreover, belief in the external world provides a simple basis for understanding the concepts of truth and reality. On the materialist hypothesis, a belief about the world, which is to say a feature of the conscious mind, is true if it conforms with an external world as demonstrated by an appropriate observational test. But since the experience of observation and confirmation will be exactly the same whether or not the material world exists independently of consciousness, the test of truth is the same for the idealist as for the materialist. Both will judge on the basis of observation that resolves to a matter of perception, a perception of a, say, a meter reading, or of the bruised foot of a philosopher who has just violently kicked a stone.
So whether an idealist or a materialist, what you consider true about the external world is what you perceive most or all candid observers to agree on. If all competent observers, material or merely perceived, agree on a fact about the world, then one has come as close as humanity is able to an awareness of reality.
For the idealist, the world is not a delusion, which is to say it is not a personal view that can be at odds with other minds real or perceived. An idealist would be delusional only if his perception of the world is at odds with that of other people, whether real or perceived.
Thus, as Pierre-Simon, marquis de Laplace is said to have told Napoleon concerning the existence of God, one may say also of the existence of the material world, "I have no need of that hypothesis." Unfortunately, the marquis de Laplace is no longer around, so we are unable to observe the shock that such a proposition might have caused him.
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