The Knowledge of Actual and Possible Beings: a discussion of Leibniz's metaphysics
W. Zachary Wolff, 2001

Leibniz presents a philosophical view in which possible worlds play an important role. While possible worlds are important in both his explanation of free will and in his argument that this is the best possible world, there is some apparent tension between the two ways in which he invokes them in his argumentation. This paper aims to illuminate and eliminate that tension, with a focus on the argument that this is the best possible world.

Leibniz's view of freedom is, roughly, as follows: Possible worlds, made up of compossible individuals, exist in the mind of God. An actual individual A's action D is free if and only if there exists a possible world, indistinguishable by any finite means, such that a possible individual P, indistinguishable from A by finite means, does not perform D. I have been unable to find an explanation of what it means for one possible world to be indistinguishable from another by finite means. Certainly the two worlds are distinguishable by finite means if in one of them an action is performed while in the other it is not. Simply watch and wait to see if the action is performed. For actions that are labeled with a specified time of occurrence, this is a finite means. Some sort of temporal clause must be added so that all that is required is that the two worlds be indistinguishable before the action.

This view does not actually explain freedom. All Leibniz has provided is a means of distinguishing free actions from unfree actions. We are left wanting an explanation of how a person wills something to happen. Leibniz's account of free will reads more like a distraction. Asked, 'How is it that we act freely?' Leibniz spins an interesting yarn about possible worlds. It seems that at the end of his tale he is left saying something like, 'If an action met these requirements, wouldn't it really look like the action was done freely?' I answer in the affirmative, but my understanding of free will is no better than it was before Leibniz's story began.

Leibniz explains causation in general as one monad (the cause) coming to bear a more clear and distinct representation of the state of another (the effect). Under this view, causation is only metaphorical. No monad actually acts on another monad. Thus, when a person acts freely the monad representing that person, his entelechy, comes to bear a more clear and distinct representation of the action in question. Presumably, the account is importantly different for unfree actions. In an unfree action, the cause would not be the entelechy of the person in question. Some other monad would play the role of coming to bear a more clear and distinct representation of the action. I find nothing in Leibniz's writing that links his view of causation with his view of freedom. This seems to me to be a rather natural way of describing freedom in Leibniz's framework, and it is completely orthogonal to the possible-worlds explanation. Whether an agent's entelechy bears an increasingly clear and distinct representation of an action he performs has no natural connection to whether or not there are possible individuals indistinguishable from the agent that do not perform the action.

Leibniz's argument that this is the best possible world is, roughly, as follows: Possible worlds, made up of compossible individuals, exist in the mind of God. Every possible thing is striving for existence as part of its essence, or perfection. God freely chooses to make actual that possible world which contains the most perfection. This world is actual. Therefore, this world is the most perfect of all possible worlds. This is an a priori argument.

The tension that arises comes from the fact that many of the possible, but not actual, worlds contain people very much like Leibniz, each of whom could make the above argument. Because the argument is meant to be a priori, its validity cannot rest on considerations about the world in which it is made. However, the argument can only be correct in one world, namely the actual world. I think the turning point in the argument, for our purposes, comes in the line, "This world is actual." This premise is true when thought by the actual Leibniz, false when thought by every other possible Leibniz.

How can we distinguish the actual Leibniz from the possible? One way out is to admit that we cannot. In this case Leibniz's conclusion must be reduced from "This is the best possible world" to "The actual world is the best possible world." I find this option rather inviting. However, I will attempt to argue for the stronger conclusion.

To show that we are justified in thinking, "This world is actual," while other possible beings are not, it is useful to reflect on Descartes' cogito. If I can establish that I exist in an actual sense, rather than merely a possible sense, it surely follows that the world I inhabit must also exist in an actual sense, even if it is left as possible that the world I inhabit may be exhausted by me. The cogito tells us that we can never doubt the existence of our self, our "I". We can doubt many things about its nature, but never its existence. This is because the action of doubting requires a doubter, namely "I".

I hold that the cogito is meant to conclude that I exist in an actual sense, not merely in a possible sense. Can we show that a merely possible Leibniz is not justified in believing in his own actual existence? When merely possible Leibniz thinks, "I think, therefore I am," he must be thinking something different than what actual Leibniz thinks when he thinks, "I think, therefore I am." In Leibniz's view of the world, every individual substance reflects the entire world in which it exists. So merely possible Leibniz reflects his merely possible world. Although these worlds may be indistinguishable by finite means, they are different. If this were not true we could not speak of two different worlds and two different Leibnizs. Crucially, the worlds are different in that one is more perfect, and thus exists, while one is less perfect, and thus is only possible. This difference will inevitably be reflected in the Leibnizs and their thoughts. In fact, this difference must be enough to make the thoughts of one true and the thoughts of the other false. So the merely possible Leibniz is not justified in his belief.

It remains to be shown that we are justified in our belief, that is, that we can somehow tell that we exist in an actual sense. I think it must be admitted that a merely possible Leibniz would be under the illusion of his being actual. How then do we know that we are not under the same illusion? One recourse is to look at how we constructed our conception of possible worlds, that is, as objects much like this world. It is assumed from the beginning that this is the actual world. How could it be anything else? If my existence, confirmed by the cogito, is not actual, then I do not even know what 'actual' is supposed to mean.

Another answer may be found in our conscious experience. Possible Leibniz cannot have conscious experience of his world in the sense of having qualia attached to his mental states. At least he cannot have a conscious experience anything like ours. Conscious experience must be reserved by God for those things he makes actual. The merely possible Leibniz is only a zombie. We have our justification for the cogito, and thus for our belief that this is the best possible world, in our moment to moment qualitative experience of our own existence.

The question really at hand here is this: What is the difference between actual and possible worlds? We know that possible worlds exist in the mind of God. The actual world also exists in the mind of God. I do not think it fits within Leibniz's metaphysics to say that the actual world exists outside the mind of God. Everything that is is in the mind of God. In what way does the actual world exist more so than the many possible worlds? What does God do when he freely chooses to make the most perfect world actual? I can find nothing in Leibniz's writings to clarify this issue. Perhaps the distinction is supposed to need no explanation. This world is obviously the actual world. To discuss any other option is nonsense.