‘Suppose I am pricked with a pin, I ask, is the _pain_ I feel a sensation? Undoubtedly it is. There can be nothing that resembles pain in an inanimate thing: the pain must be in me, a living being. But I ask again, is the _pin_ a sensation? To this question I feel myself under a necessity of answering that the pin is not a sensation, nor can have the least resemblance to any sensation. The pin has length and thickness, figure and weight. A sensation can have none of these qualities. I am not more certain that the pain I feel _is_ a sensation than that the pin _is not_ a sensation. Yet the pin is an object of sense; and I am as certain that I perceive its figure and hardness by my senses as that I feel pain when I am pricked by it.’ This is to say that if, with the philosophers, I _call_ the pin as well as the pain a sensation or an idea, I must mean by ‘sensation’ and ‘idea,’ when I apply those words to the pin, not a private self-contained feeling or a fancy, in which I am only manifesting my conscious self, but (so to speak) a _public_ sensation or idea—perceivable by other persons as well as by me—a manifestation, in short, of what is _outside my mind_—of something that exists permanently in _space_ and not transitorily in _me_—and that is thus fit to be a medium of communication between me and other living persons, informing me of their existence and in some measure of their thoughts—all which (Reid takes for granted) each person’s private feelings and fancies could not do. But to employ the words ‘sensation’ and ‘idea’ in this new meaning, and to speak of an idea as public or external, would be an abuse of language. We must mark, always by appropriate words, distinctions which we are obliged to acknowledge in fact. The inspirations or revelations of the common sense, in and through which the Almighty Power gives us an understanding of the life and world in which we find ourselves, inspirations in which all men are believed more or less to participate, require us to distinguish the solid and extended pin, as something public or outward, in contrast to the private feeling of pain, of which no one except the person who feels it is conscious. I am thus obliged to recognise more in existence than my own sensations and ideas—as much obliged as I am to recognise my sensations and ideas themselves when I am conscious of them. Only so can I find myself living in an environment that is capable of signifying the contemporaneous life, and some of the thoughts and feelings of other persons. In all this I am only falling back on the divine revelations of the common sense. They make me reject in conduct what is inconsistent with them; although this natural obligation is all the reason I can give in justification of my obedience.