To: Katherine A.
From: Geoffrey Klempner
Subject: Are possible worlds really real?
Date: 26 September 2005 13:33

Dear Katherine,

Thank you for your email of 13 September, with your first essay for the Possible World Machine, in response to the question, 'Are Possible Worlds Really Real?'

I liked your example of the newsagent with the one remaining copy of Philosophy Now, and all the different ways in which you might have not found out about Pathways.

One question you raise is whether it is really the case that you might not have purchased a copy of Philosophy Now. As you correctly anticipate, the fatalist would say, No. According to the fatalist, everything that happens in the world had to happen as it did, for the simple reason is that any statement which we make about the future already has a truth value.

The fatalist will say that the day before you purchased a copy of Philosophy of Now, it was true that in a day's time you would purchase a copy of Philosophy Now. A thousand years before you purchased a copy of Philosophy Now it was true that in a thousand years time you would purchase a copy.

For the fatalist, the future is just as much a matter of fact as the past. The only difference is we do not know the future until it happens.

In these terms, one cannot even raise the question about possible worlds. Nothing is 'possible' except what actually happens. There are no 'possible but not actual' worlds, so it is empty to raise the question whether such worlds would be real, really real, or unreal.

But suppose we 'bracket' the question of fatalism. Bracketing is something that philosophers do to focus on a specific problem. Let's say we don't know whether fatalism is true or false, but the problem we are investigating is how we should view possible worlds if fatalism is false.

If fatalism is false, then it is possible that you might not have purchased a copy of Philosophy Now. What does that statement mean? What are the conditions under which that statement would be true?

This is a problem which has been much debated by contemporary philosophers. One plausible view is that a 'possible world' is just a description, something made out of words which we might read in a book. 'Katherine decided not to visit the newsagent.' When we talk about possible worlds we are just talking about situations which we create out of words which do not correspond to what actually happened. Another view, similar to this, is that a 'possible world' is just a situation you picture in your mind, perhaps when you read words in a book, or perhaps one which you create yourself. In your mind is the scenario of your glancing at the newsagent shop and deciding that you do not have time to go in.

A difficulty raised for this approach in unit 1 is that statements which we make about things that might have been are regarded as true or false. A statement is true or false depending on the facts. Statements about what actually happened are made true or false by facts about the actual world, therefore statements about what might have happened are made true or false by facts about worlds other than the actual world. - Is that a good argument?

According to one of the strongest defenders of the 'reality' of possible worlds, David Lewis, the 'KA' who might have passed by the newsagent shop is not you but your 'counterpart'. She is very much like you, but she exists in another possible world and you exist in this world. This meets your objection against being a 'player in several possible worlds at the same time'.

But in what sense can we talk about a single, 'actual' world? You make a valid point that for all practical purposes there is not one world by many worlds - arguably, a world for each individual person. No two personal 'worlds' are exactly the same. What is interesting about this idea is that makes a rather neat parallel with what we want to say about the relation between 'the' actual world and other possible worlds.

Every personal world is equally 'real', but only one personal world is 'my world'. The difference between 'my world' and 'your world' is merely one of perspective. I am already inside my world, whereas I can only get inside yours by making an effort of sympathetic imagination. Similarly, Lewis argues, every possible world is equally 'real', but only one possible world is 'our world'. We are already inside the actual world, whereas we have to make an effort of sympathetic imagination to get inside other possible worlds, e.g. the world where you passed by the newsagent, or the world where Hurricane Katrina blew itself out before it reached the coast.

But are these worlds which we imagine 'really real' or do they just exist in our heads? Many people would prefer to believe that one 'real' world is enough. I am dissatisfied with both alternatives. I believe in possibilities - real possibilities and not just pictures which we make in our heads or words which we write on paper - but real possibility is not just another kind of 'actuality', which would be the case if we accepted Lewises theory.

All the best,

Geoffrey