Buridan's ass

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Buridan's ass is the common name for the paradox which states that an entirely rational ass, placed exactly in the middle between two stacks of hay of equal size and quality, will starve 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, however, 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 in order more fully to 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:

[I]t 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

Other writers have opted to deny the validity of the illustration. A typical counter-argument is that rationality as described in the paradox is so limited as to be a straw man of the real thing, which does allow the consideration of meta-arguments. In other words, it's entirely rational to recognize that both choices are equally good and arbitrarily pick one instead of starving. This counter-argument is sometimes used as an attempted justification for faith. The argument is that, like the starving ass, we must make a choice in order to avoid being frozen in endless doubt. Other counter-arguments exist.

Buridan's ass sometimes finds mention in electrical engineering. Specifically, in digital logic, an analog-to-digital converter must convert a continuous voltage value into either a 0 or a 1. The voltage value represents the position of the ass, and the values 0 and 1 represent the bales of hay. Like the situation of the starving ass, there exists an input on which the converter cannot make a proper decision, resulting in a metastable state. Having the converter make an arbitrary choice in ambiguous situations does not solve the problem, as the boundary between ambiguous values and unambiguous values introduces another binary decision with its own metastable state. In the ass illustration, the ass cannot decide whether or not to choose arbitrarily and so starves to death.

[edit] See also

[edit] References

  • Zupko, Jack (2003) John Buridan. Portrait of a Fourteenth-Century Arts Master. Notre Dame, Indiana: University of Notre Dame Press. (cf. pp. 258, 400n71)
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