Episode 75: Malte Willer discusses non-monotonic logic

This month, we discuss non-monotonic logic with Malte Willer, assistant professor of philosophy at the University of Chicago. Click here to listen to our conversation.

Malte WillerIf you have been so lucky as to take an introductory logic class, then you will learn a conception of logic that is, well, downright logical. That conception of logic is monotonic. Here’s what we mean by “monotonic”: You will learn that if a conclusion follows from certain information, then more information won’t affect your conclusion. Consider this example: Suppose that per your college, if you take six philosophy classes, then you can minor in philosophy. Then if you know you’ve taken six philosophy classes, you should be able to conclude that you can minor in philosophy. Additional information — say, about the many other classes you have taken — should not affect your conclusion. Well and good. (After all, who wouldn’t want to study philosophy?)

But: What if those many other classes you have taken are also in philosophy, so that in total you have taken sixteen philosophy classes? And what if you must then not minor but major in philosophy? Then a conclusion — that you can minor in philosophy — does follow from certain information, namely, that you’ve taken six philosophy classes; but more information — about your ten extra philosophy classes — invalidates that conclusion! Still, do not despair: You have motivated non-monotonic logic.

Of course, deeper motivation for non-monotonic logic abounds. For, we often use logic to help us reach reasonable but tentative conclusions, which can change with more information. Join us as Malte Willer elucidates such motivation, and its logic!

Dominic Surya






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