What do we mean when we say a thing is savory? Simply, that it produces an agreeable impression upon our palate; and the same is true of smell. Therefore, the two words, odorous and savory, express only the _causality_ of these sensations resident in the external object. We may say the same of color, for, although we commonly transfer the sensation to the object, and openly contradict the philosophical theory of light and color, this contradiction is less real than apparent; for the judgment well examined is found to consist only in referring the impression to determinate objects; so that when we for the first time hear professors of physics tell us that colors are not in the object, we easily accustom ourselves to reconcile the philosophical theory with the impression of the sense; especially since this theory does not render it less true that this or that impression comes to us from this or that object, or its different parts. 40. Here, it is not difficult to explain the phenomena of sensation or their correspondence with external objects; for the correspondence is saved if these objects be really the cause (or occasion) of the sensations. The question of extension is more difficult; for this is as the basis of all other sensible properties; and abstracting its constituting or not constituting the essence of bodies, it is certain that we know no body without extension. 41. The following observation will render palpable the difference between extension and other sensible qualities. He who has never thought of the relation of external objects to his sensations is indescribably confused; he in some sense transfers color, odor, taste, and even sound, to objects themselves, and considers confusedly these things to be qualities inherent in them. Thus the child and the uneducated man believe the color green to be really in the foliage, odor in the rose, sound in the bell, taste in the fruit. But this is readily seen to be a confused judgment, of which they render no perfectly clear account to themselves; a judgment which may be changed or even destroyed without changing or destroying the relations of our sensations with their objects. Even at a very tender age we easily accustom ourselves to refer color to light, and even not to fix it definitively, but to regard it as an impression produced upon our sense by the action of that mysterious agent. It costs us no more to consider smell as a sensation produced by the action of the effluvia of bodies upon the organ of smell; we also cease to consider sound as something inherent in the sonorous body, and come to see in it only the impression caused upon the sense by the vibration of the air, excited in its turn by the vibration of the sonorous body.