The attack on matter

George Berkeley (1685–1753), an Irish bishop, begins exactly where Locke does: all our knowledge comes through perception, and what perception delivers is ideas. A colour, a sound, a smell, a felt warmth — these are the raw materials of experience. Berkeley accepts this empiricist starting point completely. What makes him explosive is that he follows it further than Locke dared, to a conclusion he calls immaterialism: there is no material substance at all.

Here is the thesis, in Berkeley’s own famous slogan: esse est percipi — “to be is to be perceived.” For a sensible thing, to exist just is to be perceived. An apple is not a hidden something that causes a cluster of red, round, sweet, firm sensations; the apple simply is that cluster of sensible qualities, bundled together and given a name (Principles §1, §3).

The next move is the hinge of the whole system. A sensible quality — a shade of blue, a warmth — is an idea. And an idea, Berkeley insists, can only exist in a mind. It makes no sense to speak of a pain existing outside a sufferer, or a colour existing where no eye or mind is present. So if sensible things are collections of ideas, and ideas exist only in minds, then sensible things exist only in minds. Their being is their being-perceived. That is esse est percipi.

So what exactly is Berkeley denying? Material substance — sometimes called the substratum. This is the philosophers’ notion of an unthinking, unperceiving stuff that “supports” qualities and exists whether or not anyone perceives it: matter as a mind-independent something-in-itself. Locke still believed in it (an unknown “I-know-not-what” underlying the qualities). Berkeley says the notion is not just unknown but empty and impossible.

Argument 1 — matter is unknowable and idle. By everyone’s admission, all we ever directly perceive are ideas: colours, sounds, shapes, textures. We never perceive the alleged material substratum itself; by definition it is imperceptible. So the belief in matter is not something perception could ever confirm. And it explains nothing: even the materialist cannot say how an unthinking stuff would produce a vivid idea in a mind. Matter is therefore an unknowable, explanatorily idle posit — a wheel that turns nothing (Principles §§18–20).

Argument 2 — the notion of unperceived existence is incoherent (the Master Argument). Berkeley challenges you directly: try to conceive of some sensible object — a tree, a book — existing entirely unperceived, unconceived by any mind. Go ahead and picture it. But notice what just happened: in picturing it, you are conceiving it. The object is present to a mind — yours. You cannot so much as think of an unthought-of thing without thinking of it, which defeats the attempt. So the very idea of mind-independent existence is self-refuting (Principles §§22–24; Dialogues I).

Put the pieces together. Sensible things are collections of sensible qualities; qualities are ideas; ideas exist only in minds; and the notion of a mind-independent material substratum is both idle and inconceivable. Therefore there is no matter. The universe of sensible things is a universe of ideas existing in and for minds. This is Berkeley’s immaterialism — empiricism carried, with ruthless consistency, all the way down.