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This month, we talk to Paolo Santorio about counterfactuals, also known as statements of the form ‘If A were, then B would be.’ Click here to listen to our conversation.

Counterfactual statements, those funny conditional statements where the word ‘would’ comes after the word ‘then,’ play an absolutely central rule both in everyday commonsense reasoning and in our more formal scientific theorizing. Consider, for instance, how we talk about history. If Archduke Ferdiand hadn’t been assassinated, World War I wouldn’t have been fought. If the earth hadn’t been struck by an asteroid during the Mesozoic era, the dinosaurs wouldn’t have gone extinct. If I had lingered at home to watch the finale of my favorite TV show, I would have missed the bus this morning. Etc. We use these kinds of statements to describe our beliefs about laws or patterns in nature, or perhaps to say something about what someone can and can’t reasonably expect.

Figuring out what these statements has proven a bit tricky, because of their funny logical properties. For example, suppose I have two friends, Alice and Brenda. Individually, either one would be great for livening up a party. But since they don’t like each other, when they’re together at a party they fight all the time, and the party gets awkward. Then, the following two statements are true:

  • (1) If Alice comes to the party, it’ll be a good time.
  • (2) If Brenda comes to the party, it’ll be a good time.

But this one is false:

  • (3) If Alice and Brenda come to the party, it’ll be a good time.

That’s kind of weird. It isn’t that hard to account for, and there are well-studied logics that predict (3) not to logically follow from (1) and (2), but finding a satisfying philosophical interpretation for those logics gets us into all kinds of interesting conundrums about what a law is, what it means for one situation to be similar to another, and so forth. Join us as our guest walks us through this fascinating topic!

Matt Teichman