John Locke, in his famous "Essay,"[1] has made a distinction between the sameness of masses of inorganic matter and the sameness of organisms. That of the former, he says, consists in the sameness of their particles, while the sameness of a plant or animal does not consist in that of the particles which compose it at this time or at that, for they are in continual flux, but in the participation in the one life of the organism. It does not, however, appear to me that we have here a real difference in the kind of experience marked by the word. The difference is merely that in the one case we connect this experience, not with the object as a whole, but with the separate particles which compose it, which we take as so many separate objects each having a sameness of the kind just discussed, while in the other case we look upon the object as a whole, as a unit, and disregard any reference to its component parts. But whether we regard the object as a unit or take each of its ultimate parts as separate objects, we are thinking of the one kind of sameness. We are thinking of a certain life-history in which any one link may represent the whole, and any two links may be, from this point of view, regarded as equivalent. It is not merely with reference to plants and animals that we speak of sameness without regard to a sameness of constituent parts. We do it in this case simply because the organism furnishes us with a convenient unit, and one much more important as a unit than as an aggregate. We can make similar units when we please, and consider their sameness without thinking of their parts. We speak of the same nation as existing through many generations, and of the same corporation as surviving many deaths. Whether the object we are considering be naturally indivisible, or composite and assumed a unit for convenience, when we speak of it as the same at two different times we are referring to the one experience. Locke does make here a distinction worth noticing, but it does not mark two fundamentally different uses of the word. [1] Essay Concerning Human Understanding, Bk. 2, Chap. 27, § 3. SEC. 5. IV. Two objects are called the same, and two other mental experiences occurring at the one time are called the same, from the fact that they are recognized as alike. The botanist, finding that two plants belong to the one class calls them the same without any intention of confounding the two individuals. Nor does one who places his two hands in warm water and declares that he has the same feeling in both, confound the two streams of sensation. The fact that only likeness is meant is here clearly recognized. It is not, I think, as clearly recognized when similar sensations or other mental experiences (considered singly), occurring at _different_ times, are called the same. In that case they are sometimes spoken of as if they were material objects having a continuous sameness after the fashion explained above.