Randall L. Ridenour

Abstract

As I survey the beliefs that I have, I find that some of them are quite ordinary. For instance, I believe that George Washington was the first president of the US, and that a triangle has three sides. I also find that I have other beliefs, similar to the first, but with an important difference. I believe that George Washington might not have been the first president, and I believe that a triangle must have three sides. These are beliefs concerning modalities, or what is necessary and possible. Intuitively, if my belief that a triangle must have three sides is true, then there is some corresponding fact, what philosophers might call a modal fact, that makes this belief true. In this dissertation, I argue that modal facts should be analyzed in terms of the essential properties of actual objects in the world.

The concepts of necessity and possibility have been very important in the history of philosophy. For example, they play a key role in Aristotle's account of change and identity. Boethius and Duns Scotus rely on these concepts as they form their accounts of individual identity. The concept of necessity is used when formulating traditional theistic conceptions of God. The concepts are implied in Anselm's famous argument for the existence of God. Also, Descartes relied on the distinction between necessity and possibility in his attempt to prove that the mind and body are distinct. Recently, after the decline of logical positivism and ordinary language philosophy, modalities have once again become very important to philosophers. Using these concepts, Alvin Plantinga has developed powerful versions of both the ontological argument for the existence of God, and the free-will defense to the problem of evil. In order for these arguments to be successful, however, the modal concepts of necessity and possibility must be grounded in the world. If there is no basis in the world for modalities, then we have good reason to doubt the success of these arguments.

Leibniz analyzed the concept of necessity as truth in all possible circumstances or, as he picturesquely put it, truth in all possible worlds. Saul Kripke used this notion of necessity as truth in all possible worlds to develop a semantics for modal logic. As a heuristic, the concept of possible worlds has proven extremely useful in analyzing the meaning of statements using modal terms. Given this success, it is natural to think that statements about modalities are really about possible worlds. In other words, what makes the statement 'A triangle must have three sides' true is that there is no possible world in which a triangle does not have three sides. This is to say that modal facts are grounded in facts about possible worlds. An analysis of modalities, therefore, requires an analysis of possible worlds.

Broadly speaking, philosophers have taken two different positions on possible worlds. One position, associated primarily with David Lewis, is a realism about possible worlds. The realist believes that possible worlds exist, and are the same kind of thing as the actual world. Other worlds are like our world, they have people, animals, houses, and trees. The significant difference between our world and other worlds is perspectival: we are in this one, and not in the others. The others are no less real, however. It's tempting to immediately dismiss realism as too far-fetched to be true. Realism, however, has a strength that is difficult to dismiss. If realism were true, then it would be possible to explain modalities without using any language about possibility and necessity. This gives the realist theory a great deal of explanatory power.

The other position is actualism. The actualist believes that possible worlds are constructed of actually existing objects, such as obtainable states of affairs or instantiable properties. An important point is that the actualist can explain possibility only in terms of a state of affairs that possibly obtains, or a property that is possibly instantiated. Actualism loses much of the explanatory power of realism, because it is committed to a modal concept, either instantiability or obtainability, that is primitive and cannot be explained.

I argue that neither conception of possible worlds can successfully serve as the ground for modal facts. Realism, as it is found in Lewis and others, does not explain modalities without using modal concepts, but only hides the modal concepts in its theoretical language. Actualism is no more successful. In fact, no conception of possible worlds is successful, because the possible worlds theorist is committed to the following two claims: 1) There must be as many worlds as there are propositions, and 2) there must be as many propositions as there are sets of worlds. Given that there are an infinite number of possibilities, these two claims can only be true if there are more possible worlds than there are. Specifically, I argue that a possible worlds theory can serve as the ground of modal facts only if the set of possible worlds is the same size as the set of propositions, but, for purely logical reasons, this is impossible. I then argue that the concept of a world as the object that has everything else as parts is mereologically incoherent.

The only successful ground for modal facts is in the properties of actually existing objects, specifically their essential and non-essential properties. If this is right, then, the belief that there are modal facts commits one to the position known as essentialism. Recent versions of essentialism fail to provide a ground for modalities because they define essential properties as necessary properties. This immediately succumbs to a charge of circularity. What is required is a theory that defines necessary properties in terms of essential ones. The most satisfactory account can be found in Aristotle.

The task, then, requires that I examine Aristotle's account of essences in detail, and its modifications during the medieval period. Then, I develop a theory of essences that can provide a metaphysical ground for modalities. For Aristotle, the essence of a thing is the answer to a ti esti, or "what is it?", question. Once we know the correct definition of something, then we know its essence. Aristotle avoids the circularity problem, because he does not take all necessary properties to be part of the essence of a thing. His conception of essences can provide a basis for modalities, however, because the essence places constraints on the other properties that a thing can have. Some properties, although not part of a thing's essence, will be implied by the essence, in the sense that any object that has that essence will also have those other properties. Aristotle's uses a triangle for an example. The essence of a triangle is to be a three-sided closed plane figure. This essence entails the property of having interior angles equal to 180 degrees. Both are necessary, but only the first is an essential property. The essential properties and those that are implied by the essence will provide the basis for necessity. Possibilities will be defined in terms of properties that are neither implied by the essence nor contrary to the essence.

The position that things have essences has certainly been controversial. There have been several serious objections to it. The first is the problem of identity in modal contexts. In order for me to know that some properties are essential to an object, I must be able to identify that object if it had different properties than it in fact has. This certainly seems impossible to do. I show that, although this is an obvious problem for possible world theorists, it presents no real difficulty for the essentialist. In an essentialist theory, the problem of identity in modal contexts either disappears, or, at worst, it is no greater than the problem of trans-temporal identities. More troublesome are the objections raised by the empiricist tradition. W.V.O. Quine objected that an essence is relative to the description of a thing. I show that this is the case for artifacts, but not for living things. Quine's objection relies on an equivocation between de dicto modalities, necessities applied to sentences, and de re modalities, necessities applied to things themselves. Next, I address the epistemological objections to essentialism. I show that, not only do we have access to essences, but the proper role of science is to investigate essences.

Since the main body of the dissertation is primarily concerned with the essences of natural objects, I close with two appendices concerning the essences of other things in the world. First, I discuss the essences of artifacts, and show how a theory of essences can address a classic problem in philosophy, that of the Ship of Theseus. In this problem, we find that our intuitions concerning the identity of an artifact, a ship, vary relative to a context. Since the essences of artifacts are relative to a description, the essentialist can explain why our intuitions are also relative.

Next, I address the essence of the Divine. I show how ontological arguments for the existence of God are strengthened in an essentialist context. The ontological argument relies on the premise that God possibly exists. This is a very plausible premise to those of us who happen to believe the conclusion. Others, however, often object that it is impossible to demonstrate that something possibly exists short of demonstrating that it actually exists. I show that the possible existence of a thing can be demonstrated simply by showing that its essence implies no contradictions.

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