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.