To: Matthew M.
From: Geoffrey Klempner
Subject: Berkeley: to exist is to perceive or to be perceived
Date: 21 September 2007 13:00

Dear Matthew,

Thank you for your email of 10 September, with your fourth essay for Possible World Machine, in response to the question:

'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'. You have grasped the bull by the horns and constructed your explanation Berkeley's theory around this point.

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