Our question is then: What is the metaphorical sense of "modify" in which the proposition that all relations are internal is equivalent to the proposition that all relational properties "modify" the terms which possess them? I think it is clear that the term "modify" would never have been used at all to express the relation meant, unless there had been some analogy between this relation and that which we have seen is the proper sense of "modify," namely, _causes_ to change. And I think we can see where the analogy comes in by considering the statement, with regard to any particular term A and any relational property P which belongs to it, that A _would have been different from what it is if it had not had_ P: the statement, for instance, that Edward VII would have been different if he had not been father of George V. This is a thing which we can obviously truly say of A and P, in some sense, whenever it is true of P that it _modified_ A in the proper sense of the word: if the being held in the flame causes the sealing-wax to melt, we can truly say (in some sense) that the sealing-wax would not have been in a melted state if it had not been in the flame. But it seems as if it were a thing which might also be true of A and P, where it is _not_ true that the possession of P _caused_ A to change; since the mere assertion that A would have been different, if it had not had P, does not necessarily imply that the possession of P _caused A_ to have any property which it would not have had otherwise. And those who say that all relations are internal do sometimes tend to speak as if what they meant could be put in the form: In the case of every relational property which a thing has, it is always true that the thing which has it would have been different if it had not had that property; they sometimes say even: If P be a relational property and A a term which has it, then it is always true that A _would not have been A_ if it had not had P. This is, I think, obviously a clumsy way of expressing anything which could possibly be true, since, taken strictly, it implies the self-contradictory proposition that if A had not had P, it would not have been true that A did not have P. But it is nevertheless a more or less natural way of expressing a proposition which might quite well be true, namely, that, supposing A has P, then anything which had not had P would necessarily have been different from A. This is the proposition which I wish to suggest as giving the metaphorical meaning of "P _modifies_ A," of which we are in search. It is a proposition to which I think a perfectly precise meaning can be given, and one which does not at all imply that the possession of P _caused_ any change in A, but which might conceivably be true of all terms and all the relational properties they have, without exception. And it seems to me that it is not unnatural that the proposition that this is true of P and A, should have been expressed in the form, "P modifies A," since it can be more or less naturally expressed in the perverted form, "If A had not had P it would have been different,"--a form of words, which, as we saw, can also be used whenever P does, in the proper sense, modify A.