I hope this is sufficient to make clear exactly what the conception is which I am expressing by the phrase "different in intrinsic nature." The important points are (1) that it is a kind of difference which does _not_ hold between two things, when they are _merely_ numerically different, but only when, besides being numerically different, they are also _not_ exactly alike and (2) that it is _not_ identical with qualitative difference; although qualitative difference is one particular species of it. The conception seems to me to be an extremely important and fundamental one, although, so far as I can see, it has no quite simple and unambiguous name: and this is the reason why I have dwelt on it at such length. "Not exactly like" is the least ambiguous way of expressing it; but this has the disadvantage that it looks as if the idea of exact likeness were the fundamental one from which this was derived, whereas I believe the contrary to be the case. For this reason it is perhaps better to stick to the cumbrous phrase "different in intrinsic nature." So much for the question what is meant by saying of two things that they "differ in intrinsic nature." We have now to turn to the more difficult question as to what is meant by the words "impossible" and "necessary" in the statement: A kind of value is intrinsic if and only if, it is _impossible_ that _x_ and _y_ should have different values of the kind, unless they differ in intrinsic nature; and in the equivalent statement: A kind of value is intrinsic if and only if, when anything possesses it, that same thing or anything exactly like it would _necessarily_ or _must_ always, under all circumstances, possess it in exactly the same degree. As regards the meaning of this necessity and impossibility, we may begin by making two points clear.