Nathan asked:

When we carry out a thought experiment, we can’t test the underlying philosophical hypothesis with any empirical data. So, besides logical flaws, what are the criteria for evaluating a philosophical hypothesis? And how can we benefit from thought experiments in our daily lives?

Answer by Geoffrey Klempner

Briefly, when we assess a philosophical thought experiment for ‘logical flaws’ this does not just cover formal logic but flaws in conceptualising and reasoning.

This is a big deal. In thinking about the ‘big’ questions, our thoughts are often confused, in a deep way. The mode of expression may be logical (there is no obvious self-contradiction) and yet we are enmeshed in one or other form of ‘disguised nonsense’ (to use Wittgenstein’s term: ‘My aim is: to teach you to pass from a piece of disguised nonsense to something that is patent nonsense’ Philosophical Investigations para. 464).

The aim of a philosophical thought experiment is to help you to do this. In filling out the details of the imagined scenario, you are forced to see hidden clashes or incoherencies that you weren’t aware of before, forced to ask questions that you hadn’t thought to ask before.

A thought experiment should also take account of any clash with empirical data, or at least theories formed on the basis of such data. For example, a thought experiment claiming to ‘prove’ the validity determinism would be put in question by discoveries in physics. Kant tried to do this in the ‘Analogies of Experience’ in the Critique of Pure Reason. He presented what he thought was a cast-iron proof of the necessity of determinism, but it is widely considered today that he was wrong.

So there is a two-way process here. Sometimes it takes an empirical result to make us see that we had reasoned out something wrongly a priori.

As for the use of thought experiments in our daily lives — we do this all the time. You offer to take Granny along with you for car trip to the seaside. Your wife points out that there’s no way Granny can sit in the back with her arthritis, and Uncle Joe’s legs are far too long to squash him in there. That’s a thought experiment. You didn’t need to actually try to fit Granny and Joe into the car, you could ‘see’ the result in your mind’s eye.

Of course, there’s also a question whether philosophy as such is useful in our daily lives, which I think it is. The debate over free will, for example. In that case, any philosophical thought experiment will impact on the decisions we make.

Nathan is currently following Pathways Program A The Possible World Machine.