Post date: Jul 9, 2015 3:37:10 AM
In thinking about Huayan Buddhist metaphysics, you spend a lot of time trying to figure out what people meant to say in saying that everything is mutually identical and mutually interpenetrative. One interpretation has it that they mean to say--or, at least, that their saying presupposes--that everything is internally related to everything else.
What's it mean to be internally related to another? Here's an example: Although I would not exist if my parents did not exist, it seems that my parents could exist even if I never do. A succinct way to express this is to say that my parents and I seem to be externally related to each other: one of us appears not to be necessary to the existence of the other. Somewhere in the world, there might be two people who are not externally related to each other, but are such that neither would exist unless the other exists. Perhaps some conjoined twins depend upon each other in this way. Such people, if there be any, are internally related to each other.
Intuitively, each of us is externally related to a great variety of people and internally related to very few (if any). But intuitions can be mistaken. A fun hobby is finding abstract principles, endorsed by more than a few major thinkers, that together require denying a common intuition. Here's my attempt for the intuition about internal relations.
Counterpart Theory is a thesis about identity across possible worlds. It says that, for persons, there isn't any. That is: for any person X and any distinct possible worlds U and V, if X exists in U, then X does not exist in V.
Mereological Essentialism is a thesis about whether wholes survive through changes or losses of their parts. It says that they don't. That is: for any part P and any whole W, if P is part of W, then W would not exist if P were to not exist as a part of W.
Consider this: Each of us exists in the actual world. We are parts of the actual world, and the actual world is a whole that contains each of us as a part. Suppose that Counterpart Theory is true. Then none of us exists in any other (non-actual) possible world. Beings qualitatively similar to us exist in other possible worlds, namely, our counterparts. But our counterparts are not identical to us. We are world-bound individuals. So if Counterpart Theory is true, the existence of the actual world is necessary to our existence.
If Mereological Essentialism is true as well, then the actual world is not necessary to our existence in the way that the atmosphere is. Because the actual world is a whole in which each of us are parts. And if wholes have their parts essentially, the actual world would not exist if any of its parts were not to exist. So if Mereological Essentialism is true, each of us is necessary to the existence of the actual world.
Hence, if both Counterpart Theory and Mereological Essentialism are true, then the actual world exists just if each person in the actual world exists. An immediate consequence of this internal relation between world and individual is that each person is internally related to every other person. Because, for any two individuals, the existence of each is individually necessary and sufficient for the existence of the actual world. So the existence of the one is necessary and sufficient for the existence of the other. And that's that.