Berkeley: to exist is to perceive or to be perceived
'To exist is either to perceive or to be perceived.' - How would you explain Bishop Berkeley's idealism to someone who knew nothing about philosophy?

This is a good essay. Many students are very puzzled by Berkeley's claim that his theory is intended as a 'defence against scepticism'.

I don't know what a 'real' tree is, because I have never met one, and never will. All I know is my perception of this tree and other trees like it. - This seems an open invitation to the most extreme scepticism which denies that the objects of our perception exist.

Berkeley's answer is that there is no 'real' tree, in the sense of some object or entity that exists apart from perception. All there is, is the possibility of my perceiving the tree, of enjoying my tree-perception, vouchsafed by God's unwavering attention to all the objects of his creation, which exist as nothing more than perceptions in God's mind.

This response differs from another possible anti-sceptical response which avoids the God-hypothesis altogether. Why not say that the 'possibility of my perceiving the tree' is just that and no more? There is a hypothetical statement - or list of hypothetical statements - whose truth is equivalent to the 'existence of the tree'. You know what a 'statement' is, and what 'truth' means. You know what it is for a statement to be hypothetical ('if A then B'). Why not stick with that?

The clear advantage of this theory - also known as 'phenomenalism' - is that we are not giving a hostage to fortune in positing a God whose existence the sceptic would be all-too ready to deny.

However, as Berkeley clearly saw, phenomenalism suffers from a defect which severely limits it as a theory of reality. The problem is that, on the normal understanding of what a hypothetical statement is, we do not accept that a hypothetical statement can be barely true, rather than true by virtue of some underlying non-hypothetical facts. There are no irreducibly 'if then' facts.

For example, 'If I drop this cup, it will break', that statement is true by virtue of the fact that the cup is made of a certain type of material, the floor has a certain hardness, the height is sufficient to cause an impact sufficient to break the cup. On the other hand, if I state, 'If I take a sip right now, there will be a hurricane in Japan,' you are entitled to ask me, not just how I know that my statement is true (I could just be idly speculating), but what I MEAN by that statement. What connection am I stating between the cup and the weather in Japan? What chain of causes and effects is meant to lead from the sip to the hurricane?

Maybe I'm just making a point about chaos theory. In that case, you do know what I mean. But if I say, 'No, I am not implying any chain of causes and effects. All I am saying is that my hypothetical statement might be true,' then you are entitled to say that you don't understand what claim I am making.

So God, or a concept which does similar work in grounding hypothetical facts about experiences is indispensable.

But now the question is: why does Berkeley's theory have any advantage over Descartes, who also brings in God in order to defeat the sceptic? In Descartes's theory, the 'real tree' exists because if it didn't God would be deceiving me. But God wouldn't do that because he is not a deceiver.

So now the dispute resolves into a debate between two different conceptions of God: a Berkeleian God and a Cartesian God. Berkeley's point against Descartes is that we simply do not comprehend what more God can do than provide for our perception of the tree whenever required. Anything more is pure redundancy.

You could have made the point that there are, in fact, two different kinds of scepticism: inductive scepticism and scepticism about an external world. We have been discussing scepticism about an external world. An example of inductive scepticism would be the Matrix scenario. The assumption behind the scenario is that there is a real physical world in which people are kept alive in pods and used as Duracells. Even if God exists, it is still possible that I am not really writing this email to you. All I have to go on, in deciding whether I am really 'awake' or not at this moment is my experience.

Both Berkeley and Descartes must concede that God cannot create a world where human beings are never deceived. In Meditation 4, Descartes goes to some lengths to explain why that is so. We are given organs of perception and the capacity for judgement which, if used correctly, can lead us to knowledge and truth. However, Descartes must ultimately allow that, given our finitude, there is always the possibility that we are being tricked, and even the most careful and responsible search for truth might never discover that fact.

All the best,

Geoffrey

Like John Locke before him, George Berkeley was an empiricist, meaning that he saw experience as the primary source of knowledge. This view, which can be traced back to Aristotle, stands in contrast to the rationalist view that, in principle, all knowledge can be gained through rational reflection alone. Berkeley shared the same assumptions as Locke, but reached very different conclusions. According to Berkeley, Locke’s Empiricism was moderate; it still allowed for the existence of a world independent of the senses, and followed René Descartes in seeing humans as being made up of two distinct substances, namely mind and body.
There is no such thing as what philosophers call material substance.
George Berkeley
Berkeley’s empiricism, on the other hand, was far more extreme, and led him to a position known as “immaterialist idealism.” This means that he was a monist, believing that there is only one kind of substance in the universe, and an idealist, believing that this single substance is mind, or thought, rather than matter.
Berkeley’s position is often summarized by the Latin phrase esse est percipi (“to be is to be perceived”), but it is perhaps better represented by esse est aut perciperi aut percipi (“to be is to perceive or to be perceived”). For according to Berkeley, the world consists only of perceiving minds and their ideas. This is not to say that he denies the existence of the external world, or claims that it is in any way different from what we perceive. His claim is rather that all knowledge must come from experience, and that all we ever have access to are our perceptions. And since these perceptions are simply “ideas” (or mental representations), we have no grounds for believing that anything exists other than ideas and the perceivers of ideas.
Causation and volition
If there were external bodies, it is impossible we should ever come to know it.
George Berkeley
Berkeley’s target was Descartes’ view of the world as elaborated by Locke and the scientist Robert Boyle. In this view, the physical world is made up of a vast number of physical particles, or “corpuscles”, whose nature and interactions give rise to the world as we understand it. More controversially, for Berkeley, this view also maintains that the world causes the perceptual ideas we have of it by the way it interacts with our senses.
An idea can be like nothing but an idea; a color or figure can be like nothing but another color or figure.
George Berkeley
Berkeley has two main objections to this view. First, he argues that our understanding of causality (the fact that certain events cause other events) is based entirely on our experience of our own volitions (the way we cause events to happen through the action of our wills). His point is not simply that it is wrong for us to project our own experience of volitional action onto the world—which we do when we say that the world causes us to have ideas about the world. His point is that there is in fact no such thing as a “physical cause”, because there is no such thing as a physical world beyond the world of ideas that could possibly be the cause of our ideas. The only type of cause that there is in the world, according to Berkeley, is precisely the volitional kind of cause that is the exercise of the will.
Berkeley’s second objection is that because ideas are mental entities, they cannot resemble physical entities, because the two types of thing have completely different properties. A painting or a photograph can resemble a physical object because it is itself a physical thing, but to think of an idea as resembling a physical object is to mistake it for a physical thing itself. Ideas, then, can only resemble other ideas. And as our only experience of the world comes through our ideas, any claim that we can even understand the notion of “physical things” is mistaken. What we are really understanding are mental things. The world is constructed purely of thought, and whatever is not itself perceiving, exists only as one of our perceptions.
The cause of perception
If things that are not perceivers only exist in so far as they are perceived, however, this seems to mean that when I leave the room, my desk, computer, books, and so on all cease to exist, for they are no longer being perceived. Berkeley’s response to this is that nothing is ever unperceived, for when I am not in my room, it is still perceived by God. His theory, therefore, not only depends on the existence of God, but of a particular type of God—one who is constantly involved in the world.
All the choir of heaven and furniture of earth—in a word, all those bodies which compose the frame of the world—have not any subsistence without a mind.
George Berkeley
For Berkeley, God’s involvement in the world runs deeper than this. As we have seen, he claims that there are no physical causes, but only “volitions”, or acts of will, and it follows that only an act of will can produce the ideas that we have about the world. However, I am not in control of my experience of the world, and cannot choose what I experience—the world simply presents itself to me the way it does, whether I like it or not. Therefore, the volitions that cause my ideas about the world are not mine; they are God’s. So for Berkeley, God not only creates us as perceivers, he is the cause and constant generator of all our perceptions. This raises a number of questions, the most urgent being: how is it that we sometimes perceive things incorrectly? Why would God want to deceive us?
Berkeley tries to answer this question by claiming that our perceptions are never, in fact, in error, and that where we go wrong is in the judgements we make about what we perceive. For example, if an oar half-submerged in water looks bent to me, then it really is bent—where I go wrong is thinking that it only appears to be bent.
Optical illusions are impossible, for Berkeley, since an object is always as it appears to be. A straw submerged in water, for example, really is bent, and a magnified object really is larger.
However, what happens if I reach into the water and feel the oar? It certainly feels straight. And since the oar cannot be both straight and bent at the same time, there must in fact be two oars—one that I see and one that I feel. Even more problematic for Berkeley, however, is the fact that two different people seeing the same oar must in fact be seeing two different oars, for there is no single, “real” oar “out there” that their perceptions converge on.
Can a tree fall over if there is nobody present to observe it? Objects only exist while they are perceived, according to Berkeley. However, the tree can fall over—because the tree, and the rest of the world, is always perceived by God.
The problem of solipsism
An inescapable fact of Berkeley’s system, therefore, seems to be that we never perceive the same things. Each of us is locked in his own world, cut off from the worlds of other people. The fact that God has an idea of an oar cannot help us here, for that is a third idea, and therefore a third oar. God caused my idea and your idea, but unless we share a single mind with each other and with God, there are still three different ideas, so there are three different oars. This leads us to the problem of solipsism—the possibility that the only thing I can be certain of existing—or that may in fact exist—is myself.
One possible solution to solipsism runs as follows: since I can cause changes in the world, such as raising my own hand, and since I notice similar changes in the bodies of other people, I can infer that those bodies are also changed by a “consciousness” inside them. The problem for Berkeley, though, is that there is no “real” hand being lifted—the most a person can do is be the cause of the idea of his own hand rising—and only their idea, not another person’s. I, in other words, must still rely on God to supply me with my idea of another person’s hand rising. Far from supplying us with empirical certainty, therefore, Berkeley leaves us depending for our knowledge of the world, and of the existence of other minds, upon our faith in a God that would never deceive us.
George Berkeley
George Berkeley was born and brought up at Dysart Castle, near the town of Kilkenny, Ireland. He was educated first at Kilkenny College, then at Trinity College, Dublin. In 1707 he was elected a Fellow of Trinity, and was ordained an Anglican priest. In 1714, having written all his major philosophical works, he left Ireland to travel around Europe, spending most of his time in London.
When he returned to Ireland he became Dean of Derry. His main concern, however, had become a project to found a seminary college in Bermuda. In 1728 he sailed to Newport, Rhode Island, with his wife, Anne Foster, and spent three years trying to raise money for the seminary. In 1731, when it became clear that funds were not forthcoming, he returned to London. Three years later he became Bishop of Cloyne, Dublin, where he lived for the rest of his life.
Key Works
1710Treatise Concerning the Principles of Human Knowledge
1713Three Dialogues Between Hylas and Philonous