Buridan's Ass

Buridan's Ass is the name given to a paradox: that a hungry and thirsty ass placed exactly in the middle between water and hay will be unable to choose because neither choice is preferable or closer; he will therefore die of thirst and hunger. The paradox is named for Jean Buridan (c.1300-c.1361), who studied and taught at the University of Paris. He had a reputation for being a bright and charismatic figure who had a way with the ladies, but that last part might have been spread by his detractors.

But Buridan, who wrote several works including answers to puzzles such as the liar paradox, never discussed the dilemma of the ass; he might have, because it had been around for hundreds of years.

Aristotle mocked the paradox in his De Caelo (On the Heavens). There was an idea circulating that one could explain the unmoving nature of the Earth simply because it was round and centered among all that existed, and therefore all forces acted upon it equally, maintaining an equilibrium. Aristotle mocked this idea by saying it was as ridiculous as if to say that "a man, being just as hungry as thirsty, and placed in between food and drink, must necessarily remain where he is and starve to death." Other early philosophers commented in this dilemma as well.

Why did it get ascribed to Buridan? In his works, he does consider that a rational choice could not be made by a rational person between two equally good options:

Should two courses be judged equal, then the will cannot break the deadlock, all it can do is to suspend judgement until the circumstances change, and the right course of action is clear.

This was just a "thought experiment" for him, however. He did not believe this would in fact lead to total inaction: he believed in a moral determinism that would lead one to a choice, even though that choice or preference might come through an unknowable thought process. Later writers mocked him by laying the burden of the ass paradox on him.

Buridan and Aristotle would cross paths on another issue, however: when a thrown object leaves the hand of the thrower, what keeps it moving? Aristotle had a theory that was clung to by many for centuries. Buridan had a different idea, one that anticipated Newton by about 300 years.

But that's a story for another day.