The new problem of knowledge

The moderns inherit a single fateful assumption, so widely shared that Locke, Berkeley, and Hume simply build on it: the immediate objects of the mind are ideas — mental representations — not external things themselves. When you look at a tree, what is directly present to your awareness is a visual idea of a tree; the tree out in the world is, at best, its cause. This is the representational theory of perception, and the moderns call it the way of ideas.

This assumption generates the defining problem of the era: the veil of ideas (or veil of perception). If ideas are what we directly perceive, then ideas stand between the mind and the world like a veil. And now a sceptical gap yawns open: how can I ever know that my ideas resemble, or are even reliably caused by, a reality outside my mind? To check would require comparing idea and object — but I only ever have access to the idea. I can never get behind the veil to look.

Why did the new science force this inward turn? Because of the primary/secondary quality distinction. The mechanical philosophy said the real, mind-independent world consists only of matter in motion — things with size, shape, position, number, and motion. These are the primary qualities, and they belong to bodies themselves. But what about colour, sound, taste, smell, warmth? On the new physics, these are not out there in the objects at all.

Take colour. Physics describes the world as colourless particles reflecting light of various wavelengths. The redness you experience is not a property of the surface; it is an idea produced in you by the surface’s primary qualities acting on your sense organs. Colour, sound, and the rest are secondary qualities: powers in objects to cause certain sensations in us. The rose is not red in the dark; it merely has the standing power to look red. Warmth is in you, not in the fire.

Notice how this deepens the veil problem. Even for primary qualities, all I directly have is my idea of shape or motion — and I am now told that at least some of my ideas (the secondary ones) resemble nothing in the object. So which of my ideas track reality and which are mere productions of my mind? The felt world I actually live in turns out to be, in large part, a construction, and the “real” world recedes behind it.

Into this anxious situation comes a second force: the revival of ancient skepticism. In the 16th century, the writings of Sextus Empiricus — the great compiler of Greek Pyrrhonian skepticism — were recovered, translated, and widely read. The Pyrrhonist’s arsenal of arguments aimed to show that for every claim a counter-claim can be balanced, so we should suspend judgement (epochē) about how things really are.

The era’s characteristic response to all this is foundationalism. The picture is architectural: knowledge is a building. Some beliefs are foundations — held not on the basis of any other belief, and (the hope is) immune to doubt. All other knowledge is superstructure, resting on the foundations by secure inference. Find the indubitable foundations, build carefully upward, and you get knowledge that scepticism cannot shake.

So the stage is set, and the stakes are enormous. If the veil of ideas cannot be pierced, then everything is thrown into question: the external world (is there anything beyond my ideas?), God (can I prove a reality that guarantees my ideas?), and even the self (what am I, the thing having all these ideas?). The next lesson introduces the two great strategies for answering — reason and experience — that split the moderns into rationalists and empiricists.