WHEN we taste any solid or liquid substance, we have always two distinct perceptions: first, that of the solid or liquid body, which is naturally felt as pressing upon, and therefore as external to, and independent of, the organ which feels it; and secondly, that of particular taste, relish, or savour which it excites in the palate or organ of Tasting, and which is naturally felt, not as pressing upon, as external to, or as independent of, that organ; but as altogether in the organ, and nowhere but in the organ, or in the principle of perception which feels in 445 that organ. When we say that the food which we eat has an agreeable or disagreeable taste in every part of it, we do not thereby mean that it has the feeling or sensation of taste in any part of it, but that in every part of it, it has the power of exciting that feeling or sensation in our palates. Though in this case we denote by the same word (in the same manner, and for the same reason, as in the case of heat and cold) both the sensation and the power of exciting that sensation, this ambiguity of language misleads the natural judgments of mankind in the one case as little as in the other. Nobody ever fancies that our food feels its own agreeable or disagreeable taste.
EVERY smell or odour is naturally felt as in the nostrils; not as pressing upon or resisting the organ, not as in any respect external to, or independent of, the organ, but as altogether in the organ, and nowhere else but in the organ, or in the principle of perception which feels in that organ. We soon learn from experience, however, that this sensation is commonly excited by some external body; by a flower, for example, of which the absence removes, and the presence brings back, the sensation. This external body we consider as the cause of this sensation, and we denominate by the same words both the sensation and the power by which the external body produces this sensation. But when we say that the smell is in the flower, we do not thereby mean that the flower itself has any feeling of the sensation which we feel; but that it has the power of exciting this sensation in our nostrils, or in the principle of perception which feels in our nostrils. Though this sensation, and the power by which it is excited, are thus denoted by the same word, this ambiguity of language misleads, in this case, the natural judgments of mankind as little as in the two preceding.
EVERY sound is naturally felt as in the Ear, the organ of Hearing. Sound is not naturally felt as resisting or pressing upon the organ, or as in any respect external to, or independent of, the organ. We naturally feel it as an affection of our Ear, as something which is altogether in our Ear, and nowhere but in our Ear, or in the principle of perception which feels in our Ear. We soon learn from experience, indeed, that the sensation is frequently excited by bodies at a considerable distance from us; often at a much greater distance, than those ever are which excite the sensation of Smelling. We learn too from experience that this sound or sensation in our Ears receives different modifications, according to the distance and direction of the body which originally causes it. The sensation is stronger, the sound is louder, when that body is near. The sensation is weaker, the sound is lower, when that body is at a distance. The sound, or sensation, too undergoes some 446 variation according as the body is placed on the right hand or on the left, before or behind us. In common language we frequently say, that the sound seems to come from a great or from a small distance, from the right hand or from the left, from before or from behind us. We frequently say too that we hear a sound at a great or small distance, on our right hand or on our left. The real sound, however, the sensation in our ear, can never be heard or felt any where but in our ear, it can never change its place, it is incapable of motion, and can come, therefore, neither from the right nor from the left, neither from before nor from behind us. The Ear can feel or hear nowhere but where it is, and cannot stretch out its powers of perception, either to a great or to a small distance, either to the right or to the left. By all such phrases we in reality mean nothing but to express our opinion concerning either the distance or the direction of the body which excites the sensation of sound. When we say that the sound is in the bell, we do not mean that the bell hears its own sound, or that any thing like our sensation is in the bell, but that it possesses the power of exciting that sensation in our organ of Hearing. Though in this, as well as in some other cases, we express by the same word, both the Sensation, and the Power of exciting that Sensation; this ambiguity of language occasions scarce any confusion in the thought, and when the different meanings of the word are properly distinguished, the opinions of the vulgar, and those of the philosopher, though apparently opposite, on examination turn out to be exactly the same.
These four classes of secondary qualities, as philosophers have called them, or to speak more properly, these four classes of Sensations; Heat and Cold, Taste, Smell, and Sound; being felt, not as resisting or pressing upon the organ, but as in the organ, are not naturally perceived as external and independent substances; or even as qualities of such substances; but as mere affections of the organ, and what can exist nowhere but in the organ.
They do not possess, nor can we even conceive them as capable of possessing, any one of the qualities, which we consider as essential to, and inseparable from, external solid and independent substances.
First, They have no extension. They are neither long nor short; they are neither broad nor narrow; they are neither deep nor shallow. The bodies which excite them, the spaces within which they may be perceived, may possess any of those dimensions; but the Sensations themselves can possess none of them. When we say of a Note in Music, that it is long or short, we mean that it is so in point of duration. In point of extension we cannot even conceive, that it should be either the one or the other.
Secondly, Those Sensations have no figure. They are neither round nor square, though the bodies which excite them, though the spaces within which they may be perceived, may be either the one or the other.