Principles of Human Knowledge

Overview

Berkeley published this at twenty-five, in Dublin, and it is barely a hundred pages. It is numbered in short sections, written in clean eighteenth-century English, and it contains no technical apparatus at all. You can read the whole argument in an afternoon and then spend a term failing to refute it.

The subtitle tells you what he thinks he is doing: inquiring into the chief causes of error and difficulty in the sciences, with the grounds of scepticism, atheism and irreligion. Berkeley is not a sceptic and does not think he is being paradoxical. He believes that common sense is on his side and that philosophy has been wrong, because philosophers invented an unobservable substance, called it matter, placed it behind everything anyone actually sees, and then found they could not prove it was there. His solution is to delete it. Ordinary people, he insists, never believed in it in the first place.

A note on what happened to the book. This is Part I. Berkeley drafted Part II, on spirits and morality, lost the manuscript travelling in Italy, and never wrote it again. What survives of that side of his system is mostly in the Three Dialogues, published three years later, which is the same argument staged as a conversation and much easier to read.

The argument

The introduction. Before the idealism comes a demolition of abstract general ideas. Locke had said the mind forms a general idea of a triangle that is neither equilateral nor scalene nor isosceles but all and none of these. Berkeley says try it. You cannot, because there is nothing there to form. What makes an idea general is not its content but its use: a particular triangle stands in for all of them. The reason this comes first is that most of the doctrines he is about to attack survive only by hiding inside an abstraction, and none more so than the idea of existence considered apart from being perceived.

Sections 1 to 24: the core. The objects of human knowledge are ideas: what the senses deliver, what the mind notices in itself, and what memory and imagination compound out of those. Besides ideas there is the thing that perceives them, which Berkeley calls a mind, spirit, soul or self. An apple is a collection of sensible qualities that go together reliably. Every one of those qualities is an idea. So the apple is a collection of ideas, and its being is being perceived.

Then the objection everyone makes: surely the things exist when nobody is looking. Berkeley’s answer in section 23 is to ask you to try conceiving a tree that nobody perceives. You form the image, and you have been perceiving it all along. You can leave yourself out of the picture, he says, but you cannot leave yourself out of the conceiving.

In between, he takes apart Locke’s distinction between primary qualities, supposedly in the object, and secondary ones, supposedly in us. His argument is that the reasons for calling colour and taste mind-dependent, that they vary with the observer’s condition and position, apply just as well to size, shape and motion, and that anyway you cannot form an idea of extension without some colour. And section 8 blocks the retreat: whatever a material thing is, an idea could only ever resemble another idea, so the claim that our ideas copy matter cannot even be stated.

Sections 25 to 33: where sensations come from. Ideas are inert. Nothing about a patch of blue does anything. So the cause of my sensations is not an idea, and since I do not produce them, and cannot open my eyes at noon and choose what to see, the cause is another spirit. Its productions come in such constancy and order that we call them the laws of nature. Real things are distinguished from imagination not by being made of different stuff but by being stronger, more orderly, more coherent, and not up to me.

Sections 34 to 84: objections. The bulk of the book, and the part that shows Berkeley knew exactly how odd he sounded. Does this mean everything is illusion? Does food nourish us only in idea? What about the sun before there were observers? Does natural science become pointless? He answers each, and his general line is that he changes nothing about what we eat, see, predict or say, only about what we think lies behind it.

Sections 85 to 156: consequences. Against matter, against infinitesimals and abstraction in mathematics, and then the striking attack on Newton’s absolute space and absolute motion, which Berkeley says are further abstractions with no possible observation attached. He ends where he intended to end, with God and the soul.

How to read it

Read the introduction first, but do not get stuck in it. Its job is to disarm one particular defence, and the main event is section 1 onward.

Sections 1 to 33 are the argument. Read them twice. Then read the objections in 34 to 84 selectively, looking for the one that is yours, because it will be there.

If the treatise is hard going, switch to the Three Dialogues between Hylas and Philonous. Berkeley wrote them because the Principles was received badly, and the dialogue form forces him to put the objections in someone’s mouth and answer them at length.

Write down the step you think is wrong and keep coming back to it. Most first readers point at the identification of sensible qualities with ideas in sections 1 to 7 and then find that Locke has already conceded most of it.

The famous refutation is not one. Boswell reports Samuel Johnson kicking a large stone and declaring that he refuted Berkeley in that way. Berkeley agrees that the stone is hard, resists the foot, and will do so again tomorrow. He denies only that there is something behind the hardness and the resistance, of which nobody could have any experience whatever.

Questions it raises

• If to be is to be perceived, what keeps the room in existence when everyone leaves it? Is God’s perceiving it the same kind of thing as yours?
• Berkeley says an idea can be like nothing but an idea. Is that a discovery about resemblance, or a definition that settles the question in advance?
• He claims to be defending common sense. Does the ordinary person believe in matter, or believe nothing in particular about it?
• Science on this account describes regularities in signs rather than causes in things. Does that leave physics able to do what physics does?
• If my sensations come from another spirit, how do I know it is one spirit rather than many, or good rather than indifferent?
• Berkeley has no idea of the self, only what he calls a notion. Is that a reasonable exception, or the same move he refuses to let materialists make?