Buridan's ass is an illustration of a paradox in philosophy in the conception of free will. It refers to a hypothetical situation wherein an ass (donkey) that is equally hungry and thirsty is placed precisely midway between a stack of hay and a pail of water. Since the paradox assumes the donkey will always go to whichever is closer, it dies of both hunger and thirst since it cannot make any rational decision between the hay and water. A common variant of the paradox substitutes the hay and water for two identical piles of hay; the ass, unable to choose between the two, dies of hunger. The paradox is named after the 14th-century French philosopher Jean Buridan, whose philosophy of moral determinism it satirizes. Although the illustration is named after Buridan, philosophers have discussed the concept before him, notably Aristotle, who put forward the example of a man equally hungry and thirsty, and Al-Ghazali, who used a man faced with the choice of equally good dates. A version of this situation appears as metastability in digital electronics, when a circuit must decide between two states based on an input that is in itself undefined (neither zero nor one). Metastability becomes a problem if the circuit spends more time than it should in this "undecided" state, which is usually set by the speed of the clock the system is using. History The paradox predates Buridan; it dates to antiquity, being found in Aristotle's On the Heavens. Aristotle, in ridiculing the Sophist idea that the Earth is stationary simply because it is spherical and any forces on it must be equal in all directions, says that is as ridiculous as saying that However, the Greeks only used this paradox as an analogy in the context of the equilibrium of physical forces. The 12th-century Persian scholar and philosopher Al-Ghazali discusses the application of this paradox to human decision making, asking whether it is possible to make a choice between equally good courses without grounds for preference. He takes the attitude that free will can break the stalemate. Moorish philosopher Averroes (1126–1198), in commentary on Ghazali, takes the opposite view. Although Buridan nowhere discusses this specific problem, 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. In the face of equally good alternatives