Take an analogy: the eye is the organ of vision; by it we perceive light. Stimulate the retina in any way, and we are conscious of the sensation of light; injure or destroy the eye, and vision becomes imperfect or impossible. If eyes did not exist we should probably know nothing about light, and we might be tempted to say that light did not exist. In a sense, to a blind race, light would not exist—that is to say, there would be no sensation of light, there would be no sight; but the underlying physical cause of that sensation—the ripples in the ether—would be there all the time. And it is these ethereal ripples which a physicist understands by the term "light." It is quite conceivable that a race of blind physicists would be able to devise experimental means whereby they could make experiments on what to us is luminous radiation, just as we now make experiments on electric waves, for which we have no sense organ. It would be absurd for a psychologist to inform them that light did not exist because sight did not. The _term_ might have to be reconsidered and redefined; indeed, most likely a polysyllabic term would be employed, as is unfortunately usual when a thing of which the race in general has no intimate knowledge requires nomenclature. But the thing would be there, though its mode of manifestation would be different; a term like "vision" might still be employed, to signify our mode of perceiving and experiencing the agency which now manifests itself to us through our eyes; and plants might grow by the aid of that agency just as they do now. So, also, brain is truly the organ of mind and consciousness, and to a brainless race these terms, and all other terms, would be meaningless; but no one is at liberty to assert, on the strength of that fact, that the realities underlying our use of those terms have no existence apart from terrestrial brains. Nor can we say with any security that the stuff called "brain" is the only conceivable machinery which they are able to utilise: though it is true that we know of no other. Yet it would seem that such a proposition must be held by a materialist, or by what can be implied by the term "monist," used in its narrowest and most unphilosophic sense—a sense which would be better expressed by the term materialistic-monist, with a limitation of the term matter to the terrestrial chemical elements and their combinations, _i.e._, to that form of substance to which the human race has grown accustomed—a sense which tends to exclude ethereal and other generalisations and unknown possibilities such as would occur to a philosophic monist of the widest kind.