We all think there are ways things might have been. I might now be sunning myself on a beach in Italy instead of slaving over a hot laptop. Or I might now be asleep in bed. In fact there are a potentially infinity of things I might have been doing.
There are also a potentially infinity of things I might have been. So instead of being Director of Studies in Philosophy at OUDCE, I might have become a teacher, or a lawyer, or I might have married Prince Charles and be opening hospitals (OK some are more likely than others!).
We also think that there are things that would be the way they are no matter what. So I might have been any of the things above, but I couldn’t have been male or a hippopotamus or a paper clip. If this is right then I am necessarily female and human.
Another way in which we talk and think about possibilities is when we use counterfactuals. These are conditional sentences with false antecedents. So this is a counterfactual:
If I had been born and lived all my life in Germany I would be able to speak German
I was not born in Germany, have never lived there and do not speak German. But surely this counterfactual is true isn’t it?
And here is the problem. What on earth makes this counterfactual true? And what makes it true that I might have been a lawyer or sunning myself on an Italian Beach?
Clearly it is nothing I can perceive, indeed nothing that is actual unless, that is, possibilities are actual.
But if possibilities are actual, what exactly are they? What is their nature?
This is a major question in metaphysics.
Some people are realists about possibility. For example Some people would take a leaf out of the book of the philosopher Alexius Meinong. Meinong argued that there unactualised possibles. He meant that there exist things that don’t exist. Indeed he even thought there exist things that can’t exist (such as square circles).
Clearly if the Meinongians are to avoid contradiction they must distinguish different forms of existence. There is the sense in which you and I exist. Then there is the sense in which Pegasus or Hamlet exist.
But to embrace this theory is to face a lot of problems. Occam, for example, would be turning in his grave – if we introduce unactualised possibilities into our ontology (our list of what exists) then where do we stop? Does anything I can think about exist? Surely that means the things that exist are never-ending?
And if Sherlock Holmes exists (in whatever sense) then there ought to be facts that determine such things as whether he has three buttons on his waistcoat or not. But clearly there are no such facts. How do we reconcile the ‘gappiness’ of unactualised possibilities with our usual concept of something that exists?
David Lewis rejects Meinongianism. He thinks the only things that exist are actual. So there are no unactualised possibles. But don’t relax and think everything is OK because Lewis thinks instead that every world that is possible actually exists. So the world in which I am a lawyer actually exists, as does the world in which I am Prince Charles’s wife….
We might immediately think Occam would have something to say about this. But Lewis would point out that although there are lots of token worlds to admit into our ontology, his view requires that we admit only one type of thing: a possible world. And as possible worlds are just like the actual world (indeed our world is actual only in virtue of the fact we are in it) we have to admit things of this type. So Occam can be pacified.
But if all possible worlds are actual where are they? Can we see them?
The answer is no. All possible worlds are causally and spatio-temporally isolated from each other. Nothing ‘leaks’ from one world into another.
But this brings its own problems. How do we know about possible worlds? Must we admit a special faculty by which we know of possibilities and necessities? There are precedents for this of course – Kant insists we need a special faculty to see the necessity of our moral duty, so why not use a similar faculty (or even the same faculty) to discern possibility?
But how can we inhabit more than one world? If there is a possible world in which I am a lawyer, then I must exist in this world and also in that world. How is this possible? Lewis can answer this question to by appeal to his ‘counterpart’ theory – I can’t exist in more than one world – but my counterparts can.
An important thing to note in talking about possible world theory is that it is distinct from multiverse theory. The latter is a theory in physics, not philosophy. Although it, like possible world theory, talks about multiple worlds, the worlds of multiverse theory are parts of this world, they are actual. But unlike Lewis’s actual possible worlds we might one day have empirical evidence for the other physical worlds of multiverse theory. We couldn’t have empirical evidence for possible worlds, however actual they are. It is logic that tells us they exist, not our empirical theories.