presuppositions of human reason might have been correct and inevitable, whilst the tendency to deny them might have sprung from a plausible misunderstanding, or the exaggeration of a half-truth: so that the critical opinion itself, after destroying the spontaneous assumptions on which it rested, might be incapable of subsisting.

In Locke the central presuppositions, which he embraced heartily and without question, were those of common sense. He adopted what he calls a "plain, historical method", fit, in his own words, "to be brought into well-bred company and polite conversation". Men, "barely by the use of their natural faculties", might attain to all the knowledge possible or worth having. All children, he writes, "that are born into this world, being surrounded with bodies that perpetually and diversely affect them" have "a variety of ideas imprinted" on their minds. "External material things as objects of Sensation, and the operations of our own minds as objects of Reflection, are to me", he continues, "the only originals from which all our ideas take their beginnings." "Every act of sensation", he writes elsewhere, "when duly considered, gives us an equal view of both parts of nature, the corporeal and the spiritual. For whilst I know, by seeing or hearing,... that there is some corporeal being without me, the object of that sensation, I do more certainly know that there is some spiritual being within me that sees and hears."

Resting on these clear perceptions, the natural philosophy of Locke falls into two parts, one strictly physical and scientific, the other critical and psychological. In respect to the composition of matter, Locke accepted the most advanced theory of his day, which happened to be a very old one: the theory of Democritus that the material universe contains nothing but a multitude of solid atoms coursing through infinite space: but Locke added a religious note to this materialism by suggesting that infinite space, in its sublimity, must be an attribute of God. He also believed what few materialists would venture to assert, that if we could thoroughly examine the cosmic mechanism we should see the demonstrable necessity of every complication that ensues, even of the existence and character of mind: for it was no harder for God to endow matter with the power of thinking than to endow it with the power of moving.

In the atomic theory we have a graphic image asserted to describe accurately, or even exhaustively, the intrinsic constitution of things, or their primary qualities. Perhaps, in so far as physical hypotheses must remain graphic at all, it is an inevitable theory. It was first suggested by the wearing out and dissolution of all material objects, and by the specks of dust floating in a sunbeam; and it is confirmed, on an enlarged scale, by the stellar universe as conceived by modern astronomy. When today we talk of nuclei and electrons, if we imagine them at all, we imagine them as atoms. But it is all a picture, prophesying what we might see through a sufficiently powerful microscope; the important philosophical question is the one raised by the other half of Locke's natural philosophy, by optics and the general criticism of perception. How far, if at all, may we trust the images in our minds to reveal the nature of external things?

On this point the doctrine of Locke, through Descartes,[3] was also derived from Democritus. It was that all the sensible qualities of things, except position, shape, solidity, number and motion, were only ideas in us, projected and falsely regarded as lodged in things. In the things, these imputed or secondary qualities were simply powers, inherent in their atomic constitution, and calculated to excite sensations of that character in our bodies. This doctrine is readily established by Locke's plain historical method, when applied to the study of rainbows, mirrors, effects of perspective, dreams, jaundice, madness, and the will to believe: all of which go to convince us that the ideas which we impulsively assume to be qualities of objects are always, in their seat and origin, evolved in our own heads.

These two parts of Locke's natural philosophy, however, are not in perfect equilibrium. All the feelings and ideas of an animal must be equally conditioned by his organs and passions,[4] and he cannot be aware of what goes on beyond him, except as it affects his own life.[5] How then could Locke, or could Democritus, suppose that his ideas of space and atoms were less human, less graphic, summary, and symbolic, than his sensations of sound or colour? The language of science, no less than that of sense, should have been recognised to be a human language; and the nature of anything existent collateral with ourselves, be that collateral existence material or mental, should have been confessed to be a subject for faith and for hypothesis, never, by any possibility, for absolute or direct intuition.

There is no occasion to take alarm at this doctrine as if it condemned us to solitary confinement, and to ignorance of the world in which we live. We see and know the world through our eyes and our intelligence, in visual and in intellectual terms: how else should a world be seen or known which is not the figment of a dream, but a collateral power, pressing and alien? In the cognisance which an animal may take of his surroundings—and surely all animals take such cognisance—the subjective and moral character of his feelings, on finding himself so surrounded, does not destroy their cognitive value. These feelings, as Locke says, are signs: to take them for signs is the essence of intelligence. Animals that are sensitive physically are also sensitive morally, and feel the friendliness or hostility which surrounds them. Even pain and pleasure are no idle sensations, satisfied with their own presence: they violently summon attention to the objects that are their source. Can love or hate be felt without being felt towards something—something near and potent, yet external, uncontrolled, and mysterious? When I dodge a missile or pick a berry, is it likely that my mind should stop to dwell on its pure sensations or ideas without recognising or pursuing something material? Analytic reflection often ignores the essential energy of mind, which is originally more intelligent than sensuous, more appetitive and dogmatic than aesthetic. But the feelings and ideas of an active animal cannot help uniting internal moral intensity with external physical reference; and the natural conditions of sensibility require that perceptions should owe their existence and quality to the living organism with its moral bias, and that at the same time they should be addressed to the external objects which entice that organism or threaten it.

All ambitions must be defeated when they ask for the impossible. The ambition to know is not an exception; and certainly our perceptions cannot tell us how the world would look if nobody saw it, or how valuable it would be if nobody cared for it. But our perceptions, as Locke again said, are sufficient for our welfare and appropriate to our condition. They are not only a wonderful entertainment