There has been a debate by empiricists whether the notions of necessity and possibility even belong in an ontology. Others have tried to come up to the challenge of empiricists by developing modal logic.
Modal/Modality: Modal statements tell us something about what could be or must be the case.
Nothing can be rectangular and circular at the same time. (Necessary truth)
Bill Clinton left the house yesterday. (Possibly)
The heart of modal semantics is the idea of a plurality of possible worlds. They claim that this is a perfectly reasonable belief and that this helps in clarifying the concept of de dicto modality and also the notion of de re modality.
De dicto: the notion of necessity or possibility as ascribed by a proposition.
De re: the notion of a thing’s exemplifying a property necessarily or contingently.
Two different versions of possible worlds have been adopted. Some view that possible worlds provides the materials for a reductive nominalism. This is David Lewis’s approach and it requires us to accept that all possible worlds are as equally real and fully concrete entities.
Other philosophers follow a different approach illustrated by Alvin Platinga. The notion of a possible world is taken to be one element in a network of interrelated concepts including the notion of a property, a proposition, de dicto modality and de re modality. We cannot reduce the concepts to concepts outside the network, but we can clarify concepts in the network by showing their relationships to each other. This is a Platonistic view; the actual world is the maximally possible state of affairs.
Problems About Modality
Many philosophers believe there are serious issues with modal notions. Critics of modal notions tend to be empiricists and challenge that our appeal to these concepts cannot be traced back to our empirical experience of the world. They argue that experience never reveals what is necessarily the case or possibly the case, but only what is the case. The argument is simply since we don’t experience anything in the world that is modal, that we shouldn’t use modal notions. When it comes to notions of talking about the necessary or possible is merely based on language and not the nonlinguistic world. Putting it simple, that bachelors are unmarried is true only in the virtue of the meaning of the words bachelor and unmarried.
The concept of possible worlds has been something developed for dealing with modal logic. A possible worlds metaphysician would say criticism is a misplaced reaction. Even though the average person doesn’t speak of possible worlds, there is a deep intuitive roots that exist in humans and the framework of possible worlds is traced back to prephilosophical beliefs we all share.
The way that they describe this is that we have all thought about the way things may have been otherwise. What may have been different if you failed that test or got a flat tire on the way to work. We have the capacity to think of a different world that went differently than the one we are living. The term ‘possible worlds’ is merely giving a name to this idea.
Possible Worlds Nominalism
There appears to be a connection between ascriptions of both de dicto and de re modality and talk about the way things might have been, talk about various possible worlds. How do we interpret this connection? Not all possible world metaphysicians answer this question the same way. There are two main views:
One group insists that the notions of possible worlds, of propositional necessity, possibility, and contingency, and of essence and accident are all components in a network of interconnected and mutually supporting concepts. The view is that it is impossible to understand any of these concepts by reference to concepts that are not a part of the network.
Another group claim to find in the framework the resources for carrying out the reductive project of a very austere nominalism.
The opposition of these two groups is a central theme in recent metaphysics.
Possible Worlds Nominalism - David Lewis
Lewis tells us that if we want to know what kinds of things possible worlds are, we don’t need to do anything sophisticated, all we have to do is look at the actual world around us. His view is “more things of that sort, differing not in kind but only in what goes on at them.” Lewis doesn’t believe in the “actual world” as all the worlds are real, exist and are equally valid. His view of the actual world is just one of the total ways things might have been and it is nothing more than myself and all my surroundings.
Since we have all these possible worlds there could be the concrete objects of transworld individual. An individual that exists in more than one world, living their respected lives, pursuing several different goals. This is a difficult concept for people to grasp. Lewis agrees with this notion that presupposes the falsehood of the principle of Indiscernibility of Identicals. Simply put if you have a concrete object with the same properties that exist, that they have to be the same object. If world 1 individual pursues different goals than world 2 than the individual isn’t the same.
In Lewis’ view, each individual exists in just one possible world, there are only world-bound individuals. Lewis explains it as follows:
You are in the actual world and no other, but you have counterparts in several other worlds. Your counterparts resemble you closely in content and context in important respects. They resemble you more closely than do the other things in their worlds. But they are not really you. For each of them is in his own world, and only you are here in the actual world.
Actualism and Possible Worlds - Alvin Platinga
Many philosophers don’t like Lewis’ view of things as they view it more as a science fiction fantasy than anything real. Lewis’ ontology is one we might call possiblism, he holds that possible, but nonactual objects. There are also actualists like Platinga. As he sees it, the only concept of existence we have is that of a thing that actually exists. So obviously the idea of all these worlds with real concrete objects occupying space and time is science fiction.
Platinga does have a view of possible worlds, so this might all seem very strange. His view is that since he has the resources for showing how the claim that there are possible worlds that are not actual is compatible with a strong version of actualism. Platinga believes in a Platonistic account of abstract entities. On the view, all properties are necessary beings; they all exist necessarily. They are not however, all exemplified, so properties can exist even though they may not be exemplified.
This wasn’t a tough chapter to read, but the summation of information is a bit tough. The arguments presented are quite annoying and the possible world ‘games’ is a bit much. I find that people really go out of their way to correct some sort of issue in metaphysics by inventing even more strange ideas.
The possiblism presented by David Lewis seems quite stupid from the point of view of metaphysics and explaining existence. Actualism, as per the definition, seems more appropriate to me, but the actualism presented by Alvin Platinga seems like a similar version of stupid.