- Open a book or article of contemporary analytic philosophy, and you are likely to find talk of possible worlds therein. This applies not only to analytic metaphysics, but also to areas as diverse as philosophy of language, philosophy of science, epistemology, and ethics. Philosophers agree, for the most part, that possible worlds talk is extremely useful for explicating concepts and formulating theories. They disagree, however, over its proper interpretation. In this chapter, I discuss the view, championed by David Lewis, that philosophers' talk of possible worlds is the literal truth. There exists a plurality of worlds. One of these is our world, the actual world, the physical universe that contains us and all our surroundings. The others are merely possible worlds containing merely possible beings, such as flying pigs and talking donkeys. But the other worlds are no less real or concrete for being merely possible. Fantastic? Yes! What could motivate a philosopher to believe such a tale?
- I start, as is customary, with modality. Truths about the world divide into two sorts: categorical and modal. Categorical truths describe how things are, what is actually the case. Modal truths describe how things could or must be, what is possibly or necessarily so. Consider, for example, the table at which I am writing. The table has numerous categorical properties: its color, perhaps, and its material composition. To say that the table is brown or that it is made of wood is to express a categorical truth about the world. The table also has numerous modal properties. The table could have been red (had it, for example, been painted red at the factory), but it could not, it seems, have been made of glass, not this very table; it is essentially made of wood.
- Just where to draw the line between the categorical and the modal is often disputed. But surely (I say) there is some level - perhaps fundamental physics - at which the world can be described categorically, with no admixture of modality. Now, suppose one knew the actual truth or falsity of every categorical statement. One might nonetheless not know which truths are necessary or which falsehoods are possible. One might be lacking, that is, in modal knowledge. In some sense, then, the modal transcends the categorical.
Footnote 1: Truncated rather arbitrarily!
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