Authorial Round-up: George Berkeley
A Treatise Concerning the Principles of Human Knowledge (1710)
Three Dialogues between Hylas and Philonous (1713)

Posted 7 July 2006.


In these two works, George Berkeley sets forth the philosophical position for which he has become famous -- namely, the nonexistence of matter. The temptation to dismiss this doctrine as nonsense should be resisted for at least three reasons: first, Berkeley seems to have been genuinely convinced that his position was true, and his arguments were offered in good faith; second, the good Bishop's immaterialism was not merely asserted, but was promulgated alongside a bevy of fiendishly clever arguments which are, as we shall see, surprisingly difficult to refute; and third, his position, whether one accepts it or not, raises a host of interesting philosophical issues concerning, among other things, knowledge, causation, inference, and the existence of God.

His motive for rejecting the existence of matter was fourfold: he believed that belief in matter was a source of both skepticism and atheism, which he opposed; he believed that a world without matter could accomodate every experience that we have, and therefore the hypothesis of matter was superfluous; he saw that several long-standing philosophical problems would be solved by denying the reality of matter; and he held that the idea of matter was a contradiction. Let's consider each of these points in turn.

First, why should a belief in matter lead to skepticism and atheism? The latter is perhaps clearer: a belief in a material universe existing and operating without the apparent intervention of God leads some to suppose that God is an unnecessary hypothesis in an account of nature. This is as true today as it was in Berkeley's time.

As to skepticism, here we should recall an argument made by John Locke in his Essay concerning Human Understanding. Being an empiricist, Locke argued that we never have direct experience of things themselves; we only have experience of our sensations. We may argue that the sensations are caused by the things themselves, but nevertheless our immediate experience is, and can only be, of qualia. We see the color red, and infer the apple, but we experience only the color. Locke furthermore argued that certain qualities which we attribute to objects - such as color, smell, and sound - exist only in the mind, and are not properly called properties of the object. If this account of human knowledge is accepted, it has the effect of separating the mind from the things it seeks to know. We can know the sensation produced by an object, but the object itself remains hidden behind the veil of our own perceptions.

Berkeley accepted Locke's conclusion that we can know only our sensations, yet he was unwilling to grant that we therefore do not truly know the thing we seek to know.


Berkeley's solution to the puzzle was to reject the notion that there is a material substance "out there" that causes our sensations. He regarded the inference to the existence of a material substance producing our sensations as entirely unwarranted. We know, and can only know, ideas, and ideas may exist only in the mind. Therefore we can only know things that exist in the mind. Therefore we cannot know anything which does not exist in the mind. Therefore we are not justified in asserting that any such thing exists.


Berkeley doggedly maintained that immaterialism corresponds to common sense.  What, he asked, do we mean when we say that a tree exists in the yard?  We mean that if we go into the yard, we see a tree. Nothing more. Though we abstract away from those experiences to conceive the persistent existence of the tree independently of our perception, this abstraction is really just a convenient way of summarizing our belief that each time one enters the yard, one will see a tree. But the experiences are primary; the theory is there to support them.

Berkeley finds himself, then, in the peculiar position of maintaining both empiricism and idealism.  We should make experience the foundation of our reasoning, and since our experience is entirely of ideas - whether as sensations or concepts - we may affirm the existence only of ideas. And since an idea exists only by virtue of being perceived by some mind, he is able to summarize his position thus: esse est percipi, to be is to be perceived.

But may we not imagine a thing existing without its being perceived?  Can I not, for instance, imagine a tree existing on a remote, uninhabited desert island?  No, says Berkeley, for as soon as you imagine it, it is perceived by your mind. As soon as you conceive the idea, the object exists, but not without being perceived, for you yourself perceive it. This example illustrates how difficult it is to refute Berkeley. He limits us to the contents of our immediate experience, but, protest though we may, it seems we cannot get beyond that limit.

Berkeley held that the doctrine of immaterialism did not produce skepticism, and he denied that it made the world 'unreal'.  The world is just as real as it was before. The things we observe are real; they just have no material existence.  They are ideas, and we perceive them as such. And because we perceive the idea itself, we know the thing as it is.  There is no 'other' behind our sensation of which we remain ignorant; therefore we need not be led into skepticism about the reality of our knowledge of the world. "I am not for changing things into ideas," he said, "but rather ideas into things." (Dialogues, III)

Not only does immaterialism cure skepticism, it also, says Berkeley, solves perplexing problems that have bedeviled philosophy for ages.  For instance, philosophers have never been able to account for the manner in which material substance is able to produce an effect in the immaterial mind. After all, what does matter have to do with ideas? What does light of a certain energy have to do with the color red? You may make an empirical study of the brain in as much detail and with as much scientific rigour as you wish, but you will never discover the experience of the color red.  There is a gap between phenomena and qualia, a gap which remains to this day. Yet Berkeley points out, correctly it seems to me, that the gap only exists so long as you maintain the existence of phenomena as something other than qualia. We have been led into perplexity only because we were attempting to reconcile a fiction with reality.

Finally, Berkeley held that the very idea of matter was a contradiction.  This part of his argument is somewhat unclear to me. He begins by granting Locke's contention that secondary qualities of objects, such as color, exist only in the mind, and then proceeding to argue that Locke's primary qualities, such as extension and motion, also exist only in the mind. And if that is correct, then matter becomes a substance devoid of any qualities whatsoever. But what can a material substance be if it has no qualities? Nothing! But I don't think I understand this part of his argument very well.

One objection to Berkeley's account might be this: "If matter does not exist, why does everyone think it does?" To this, Berkeley has an interesting reply. He distinguishes two general classes of ideas: those over which we have control, such as the idea of a blue apple; and those over which we have no control, such as the sensation of red I experience when looking at an apple. The ideas over which I have control may be changed by an act of will; they are mutable, inconstant, and are sustained only by concentration.  On the other hand, the second class of ideas are not under my control; I cannot will the red apple to disappear.  Furthermore, the ideas not subject to my will exhibit a greater coherence and consistency than those which are so subject. I thus naturally conclude that those coherent, constant ideas have their source external to me. And this, says Berkeley, is a valid conclusion, yet is does not follow that that external source is material substance. Instead, Berkeley argues that those ideas, which, being ideas, must exist in a mind, exist and are sustained in existence by a mind whose power far surpasses our own. This is the foundation of his new proof for the existence of God.

Berkeley has some interesting things to say about causation. He denied the existence of efficient causes. When I shoot a tin can off the fence, the can does not fall because the bullet makes it fall. It falls because God, in whom all the contents of our experience subsist, has so ordained  that if a bullet approaches and impinges on a tin can in a certain manner, the can will fall. I think one could say that he replaces efficient causes with formal causes. Things are defined such that they behave in certain ways. If a implies b, and we have a, then we have b, but we would not say that a causes b. The emphasis on definition emphasizes that the world is the product of a mind, not of blind mechanism. The world has been thought in such a way that things behave consistently, and so we posit 'laws of nature' to account for this regularity, but we err if we ascribe necessity to those laws. I believe that David Hume argued much the same thing, and did so under the influence of Berkeley.

Before closing, I cannot resist making mention of two famous witticisms occasioned by Berkeley's philosophy.  The first concerns the great Samuel Johnson, who, upon being asked his opinion of Berkeley's position, responded by giving a strong kick on a large stone with the words, "I refute it thus!"  It is an endearing image (though, unfortunately for the learned Doctor, his aim is wide of the mark, for according to the terms of the argument it fails to refute anything).  The second is Ronald Knox's poetical explication of Berkeley's notion that nothing may exist without being perceived by some mind:

    There was a young man who said "God
    Must think it exceedingly odd
        If he finds that this tree
        Continues to be
    When there's no one about in the Quad."

    "Dear Sir, your astonishment's odd;
    I am always about in the Quad
        And that's why this tree
        Will continue to be
    Since observed by, Yours faithfully, God."

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