American political cartoon, circa 1900, on the debate over whether to build a canal through Panama or Nicaragua. The deliberations of Congress (choosing between a Panama canal route or a Nicaragua canal route, with allusion to Buridan's ass). New York Herald (Credit: The Granger Collection, NY), Circa 1900, Author: W. A. Rogers.

Buridan's ass is a figurative description of a man of indecision. It refers to a paradoxical situation wherein an ass, placed exactly in the middle between two stacks of hay of equal size and quality, will starve to death since it cannot make any rational decision to start eating one rather than the other. The paradox is named after the 14th century French philosopher Jean Buridan.

The paradox was not originated by Buridan himself. It is first found in Aristotle's De Caelo, where Aristotle mentions an example of a man who remains unmoved because he is as hungry as he is thirsty and is positioned exactly between food and drink. Buridan nowhere discusses this specific problem but its relevance is that he did advocate a moral determinism whereby, save for ignorance or impediment, a human faced by alternative courses of action must always choose the greater good. Buridan allowed that the will could delay the choice to more fully assess the possible outcomes of the choice. Later writers satirised this view in terms of an ass who, confronted by two equally desirable and accessible bales of hay, must necessarily starve while pondering a decision.

Some proponents of hard determinism have granted the unpleasantness of the scenario, but have denied that it illustrates a true paradox, as such, since one does not contradict oneself in suggesting that a man might die between two equally plausible routes of action. For example, Baruch Spinoza in his “Ethics”, suggests that a person who sees two options as truly equally compelling cannot be fully rational:

It may be objected, if man does not act from free will, what will happen if the incentives to action are equally balanced, as in the case of Buridan's ass? [In reply,] I am quite ready to admit, that a man placed in the equilibrium described (namely, as perceiving nothing but hunger and thirst, a certain food and a certain drink, each equally distant from him) would die of hunger and thirst. If I am asked, whether such an one should not rather be considered an ass than a man; I answer, that I do not know, neither do I know how a man should be considered, who hangs himself, or how we should consider children, fools, madmen, &c.

— Baruch Spinoza, Ethics, Book 2, Scholium.

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