No abstract ideas, no primary qualities

To defeat matter, Berkeley has to remove its supports. He identifies two Lockean doctrines propping it up: the theory of abstract ideas, and the primary/secondary quality distinction. In this lesson he dismantles both — and, he argues, once they fall, “matter” has nothing left to stand on.

First, abstract ideas. Locke held that the mind can form general ideas by abstraction: from many particular triangles I strip away what differs (this one’s size, that one’s angles) and keep only what is common, forming the idea of triangle in general. Locke even admitted the abstract triangle must be “neither oblique nor rectangle, neither equilateral, equicrural, nor scalenon, but all and none of these at once” (Essay IV.vii.9). Berkeley pounces: that is not a hard idea — it is an impossible one.

So Berkeley’s claim is that every idea we actually have is fully particular and determinate. There is no idea of “extension in general,” no colourless shape, no bare triangle. Generality, he grants, is real — but it is not a special abstract idea. It is a matter of use: a particular idea (some specific triangle I picture) can be made to represent all triangles of its sort, the way a single drawn triangle on a chalkboard stands in a geometry proof for triangles as such (Principles, Introduction §§12, 15–16).

Now the primary/secondary distinction. Recall Locke (and the corpuscularians): primary qualities — extension, shape, size, motion, solidity, number — really belong to bodies themselves, and our ideas of them resemble the bodies. Secondary qualities — colour, sound, taste, smell, warmth — are only powers in bodies to produce sensations in us; our ideas of them resemble nothing in the object. Colour is in the mind; shape is in the thing. This distinction is what lets “matter” survive as a bearer of the real, primary qualities.

Berkeley’s counter is elegant: Locke’s own arguments for demoting secondary qualities apply just as well to the primary ones. Why did Locke say colour is mind-dependent? Because it varies with the perceiver and conditions — the same water feels warm to a cold hand and cool to a hot one; a cloud is red at sunset, grey at noon. But extension, shape, size, and motion vary in exactly the same way. A mite’s foot looks tiny to us and vast to the mite; a tower looks round from afar, square up close; speed looks different to differently-moving observers. If perceiver-variation makes colour mind-dependent, it makes shape and size mind-dependent too (Principles §§14–15; Dialogues I).

Berkeley has a second, deeper argument — the inseparability argument. Try to conceive of a body having only primary qualities: pure extension and shape, with no colour, no tangible quality whatsoever. You cannot. Every shape you can imagine is coloured or felt; extension only ever comes clothed in some sensible quality. Primary and secondary qualities are inseparable in thought. So if the secondary ones are ideas in the mind (as Locke admits), the primary ones — which cannot be conceived apart from them — must be in the mind too (Principles §10).

See what has happened. If all qualities — primary and secondary alike — are ideas existing only in minds, then a body, which is nothing but its qualities, is nothing but a collection of ideas in minds. There is no residue of mind-independent, purely-primary “stuff” left over to be matter. Locke’s own distinctions, followed honestly, hand Berkeley his immaterialism. The material world does not merely become unknowable — it dissolves entirely.