Doriane asked:
What did the person who hit a stone and said ‘I refute him thus’ while disagreeing with Berkeley mean by that?
Answer by Helier Robinson
The original is as follows:
“After we came out of the church, we stood talking for some time together of Bishop Berkeley’s ingenious sophistry to prove the non-existence 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.'”(Boswell’s Life of Samuel Johnson, quoted from Wikipedia.)
One of Berkeley’s philosophic principles was esse est percipi, or to be is to be perceived. So anything imperceptible does not exist, including, in particular, material substance, or matter. Descartes was quite wrong, according to Berkeley, in positing two substances, thought and extension, (mind and matter): there is only mind. Dr. Johnson thought he was refuting Berkeley by kicking the stone and showing it to be material. But they were at cross purposes. For Johnson all experience can be divided into mind and matter: the external world is material and the internal world is mental. For Berkeley everything perceived in the external world is ideal, mental, and nothing material exists.
There is a lot to be said for esse est percipi: most of the qualities we perceive in the external world are secondary qualities, manufactured in the brain, and so ideal rather than material; also, illusions are misrepresentations of reality, and as such are in the brain and so ideal. On the other hand, external objects seem to be real, in that they exist when unperceived: when you are in deep sleep your bed seems to continue to exist, as does your body, because they are still there when you wake up. And if external objects are real in this way then they exist independently of mind, in which case they are material, or at least something other than mind, which might as well be called material. Berkeley accepted this continued existence of objects by claiming that when they are unperceived by anyone they still exist because they are perceived by God. Not a very satisfactory explanation; but neither was Dr. Johnson’s refutation very satisfactory.
Answer by Craig Skinner
It was Dr. Samuel Johnson, the English writer and author of the famous Dictionary, who kicked the stone.
Boswell, in The Life of Samuel Johnson (1791) says that he and Johnson were discussing George Berkeley’s view that matter was nonexistent and that everything in the universe is merely ideal, when ‘Johnson answered, striking his foot with force against a large stone, till he rebounded from it, ‘I refute him thus’ .’
I hope the following imaginary dialogue between Johnson (J) and Berkeley (B) will clarify the issue.
J. I refute you thus (kicking a big stone).
B. In what way?
J. Well, I felt the weight, hardness and solidity of the stone when my boot struck it. In short its substance or matter. So your talk of matter not existing is nonsense.
B. Not so fast Sam. You just said you felt the weight, hardness and solidity. But feelings are in your mind. The qualities of the stone are in your mind. And those you mention are what some call primary qualities, as contrasted with secondary ones like colour or smell. So all qualities are in a mind. They are ideas.
J. The qualities of the stone are ideas in my mind… mm… yes you could say that, I suppose, but the stone itself isn’t in my mind.
B. The stone itself you say. But what can that be. Take away all the qualities, like colour, weight, solidity, shape, texture, and what’s left. What can such a thing be that has no weight, solidity, hardness, shape or texture. How can it be a stone?
J. I see what you mean, George. A ‘bare particular’, as it were, devoid of any qualities whatsoever, would be a strange beast indeed. But hold on. can’t we then say that the stone is just the totality of its qualities, a ‘bundle of qualities’.
B. Yes, Sam, we can. That’s just what I do say. The stone is a bundle of qualities. Qualities are ideas. So, the stone is an idea composed of these simpler ideas. How else to explain what unites the qualities in the bundle if we have discounted a bare material thing that ‘bears’ the qualities or holds them together.
J. So you deny that the external world exists.
B. Of course I don’t. Any child knows there is an external world. I deny that matter exists. The world is composed of minds (including God’s mind) and ideas in them. Only these two. Minds and ideas. Simpler than your notion that there exist minds and ideas plus matter.
J. I’ll have to think about this George. If you say that stones, plants and planets are ideas in your mind, then surely other people are ideas in your mind too, and your position is solipsism, that you (your mind) and its ideas are all that exists. That’s even simpler than minds (including God’s) and ideas.
B. Ah well, no, you see. God exists, and I can prove it, and the external world is the same for all of us (finite spirits like you and me, Sam) because it exists in God’s mind.
J. It won’t wash, George. To assume God’s existence sounds like question-begging to me. And you can no more prove God’s existence than Descartes could, although you have to enlist God to make sense of other finite spirits (such as people) and an external world, just as Descartes enlisted God to guarantee the reliability of his clear and distinct ideas. No, the arguments you make against matter apply equally to other minds, and so you haven’t established idealism as opposed to solipsism.
B. (a little uneasily) Let’s leave it for now and pick it up another time. Fancy a beer?
J. Fine. Although of course we may be knocking back an idea rather than a cold, hoppy liquid.
Hume rightly said that Berkeley’s arguments ‘admit of no answer and produce no conviction’.
If you haven’t read Berkeley, do so. Begin with Three Dialogues between Hylas and Philonous. The version edited by Dancy (OUP 1998) is very good. Berkeley’s prose is concise, clear, witty, and a delight to read compared with that of many other great philosophers.
Ask a Philosopher 
Recall Richard Wilbur’s 4-line poem, “Epistemology”
I.
Kick at the rock, Sam Johnson, break your bones:
But cloudy, cloudy is the stuff of stones.
II.
We milk the cow of the world, and as we do
We whisper in her ear, ‘You are not true.’
Refuting Berkeley by kicking a stone is analogous to jumping up and down on the flat ground to refute the curvature of the Earth.
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