And now it is not difficult to guess why we employ such expressions as we do to indicate strict identity. If I habitually use the proposition "x is y" to indicate a relation between two things having similar elements and yet regarded as distinct, and look upon the proposition as justified by the similar elements, observing that, these remaining unchanged, the dissimilar elements may be very variable without affecting the truth of the proposition, what more natural than that I should go on using the propositional form when the dissimilar elements have diminished to zero—when the proposition has become "x is x"? To be sure, no one can take such a proposition literally, any more than one can soberly believe that one divided by zero results in infinity. Such expressions have their use and value, but they must be properly understood. If one uses the expression "x is x" to emphasize the fact that one is not to pass from x to any y or z—that one is to rule out all distinction or sense of difference, the use cannot be harmful. And the use of the propositional form has this great convenience: it puts a period, so to speak, to one's thinking, and prevents one from casting about for a completion of the thought. If one merely say to me "x," I shall probably take it as a subject and busy myself to find a predicate. If he say "x is x," he says really no more than x, but he makes me fix my thoughts upon x alone.
Sec. 20. In the foregoing search for the element that the kinds of sameness have in common, I have had in mind chiefly the samenesses of things immediately known. It is not necessary to repeat the search in the field of the "external." We have but the seven kinds of sameness, and whatever may be the things that are the same in these several ways, the elements I have indicated must be present if our words are to be significant. But one thing remains for me to do in this part of my monograph, and that will not detain me long. I must distinguish between sameness and identity, or rather point out to what kinds of sameness this latter word is commonly applied.
The word is often used quite loosely, but where the attempt is made to distinguish between identity and sameness in a looser sense, and to use terms with some precision, the former word serves to indicate sameness in which there is no consciousness of duality, or in which the consciousness of duality has fallen into the background and may easily be overlooked. Sameness of the first kind, for example, is spoken of as identity. This is the only kind of sameness in which there is no element of duality at all. The use of the word identity is not, however, restricted to this. Locke's inquiry concerning the identity of masses of inorganic matter, of vegetables, of animals, and of persons, has to do with sameness of the third kind on the list. In this kind of sameness there is no clear consciousness that one is dealing with more than one thing, and Locke's discussion is conducted throughout as though one were not.
It may be objected that in certain other kinds there is often no clear consciousness of duality, and yet one does not think of using the term identity. This is quite true. The two kinds mentioned have been thought worthy of special discussion by logician and philosopher, and have been given a technical name. The others have not. Still, although the word is not commonly used in such cases, it would, I fancy, seem natural to use it in a direct ratio to the degree in which the sense of duality falls into the background. Dr. Johnson would probably have been willing to say that the stone he saw himself kick was identical with the one the existence of which he wanted to prove. Bishop Berkeley could have felt only disgust at such a use of the term. Scarcely anyone, I suppose, would regard himself as speaking strictly if he called the fourth kind of sameness identity. The co-existence of the two things compared would prevent their being confounded. Without, then, attempting to assign any very exact limits to the application of a somewhat loosely used word, I may repeat my former statement that men use the word identity to mark certain kinds of sameness in which there is little or no consciousness of duality, and they are not inclined to use it to mark samenesses in which things are recognized as similar but clearly distinct.
With this I end the first part of my discussion, and I confess I draw a long breath in doing so. When I sat down to write it was with the impression that I could say all that was necessary about the kinds of sameness in a much smaller number of pages; but finding it impossible to avoid misunderstandings without being more explicit and detailed, I have had to change my plan. Now, that I am through, I must confess to myself that most persons will find this hair-splitting anything but entertaining—which would be held by the inconsiderate to furnish a presumption against the truth it contains, if ancient adages go for anything. It should be remembered, however, that the old saw which puts truth in a well does not indicate that the well may not be a dry one. With this consolatory reflection I turn to the second part of my task.
PART II.
HISTORICAL AND CRITICAL.
Those now who propose to hold mutual discussion must needs understand one another somewhat: for without this how can they have any mutual discussion? Each of their words then, must be familiar and have definite meaning, and not many meanings, but one only, and if it have more meanings than one, they must make it clear in which of these senses it is used.
Aristotle, Metaph., Book X, c. 5, § 3.
Section 21. When Heraclitus of Ephesus, moved thereto by his view of the constant flux of things, declared it impossible to enter the same river twice,[30] he evidently supposed that a river can be the same only in the first and strictest sense of the word. He denied, consequently, a right to use the word, as it constantly is used, to indicate that certain phenomena belong to a group or series, which, in its totality, is to us a single object. When we say that we have entered the same river twice we have no reference to the actual experiences of the two occasions considered merely as experiences. Of course, these are not the same, as each is itself, and they may even be somewhat dissimilar. Nor have we reference to the separate particles of which the body of water is composed. We all admit that the water in a river changes, and yet we never think of saying that the river is no longer the same. The two kinds of sameness are quite distinct, yet both are legitimate; and both were as familiar to the ancient Greek as to the modern American. Socrates was considered Socrates from boyhood through youth to manhood. The Ilissus was the Ilissus whether swollen or shrunken. The philosopher's difficulty with the river did not arise out of the fact that this kind of sameness was not perfectly well recognized in language and in common thought. It arose out of the fact that the beginnings of reflection make many things seem strange which before passed unnoticed, and sometimes lead to assertion and denial evidently contrary to experience and common sense. The unreflective man calls the river the same on two successive days, but he has no clear notion of what the word implies. In a loose way he opposes "same" to "different." Heraclitus saw that the water in a river is constantly changing. He who enters twice does not enter precisely the same body of water. What more natural, and what more fallacious, than to assert that he does not twice enter the same river?