The donkey that starved to death between two identical piles of hay.
Place a hungry donkey exactly halfway between two equal bales of hay. With no reason to prefer either, a perfectly rational animal never moves and starves. The joke was aimed at a medieval philosopher, but the puzzle about choosing without a reason is far older, and it even troubles computer chips.
The paradox is named after Jean Buridan, a 14th-century French philosopher, but he never discussed a donkey. He held a form of moral determinism: a person must always choose what they judge the greater good, and if two options seem exactly equal, the will cannot break the tie and should wait until circumstances change. Later writers mocked the view with the image of an ass, frozen between food and water, dying of both hunger and thirst while it deliberates.
The idea long predates him. Aristotle, in On the Heavens, mentioned a man equally hungry and thirsty, placed between food and drink, who would supposedly stay put and starve, though he used it as an analogy about balanced physical forces. In the 12th century the Persian thinker Al-Ghazali turned it into a question about human choice: offered two equally good dates, a man will simply take one, which Al-Ghazali saw as evidence of a will that can decide between similar things. Averroes, commenting on him, took the opposite view.
Later philosophers kept returning to this 'choice without preference'. Spinoza, a determinist, accepted that a person in such perfect balance might indeed starve. Pierre Bayle pointed out that everyday life is full of choices where the options don't matter to us, and we manage them without trouble. Leibniz suggested that tiny unconscious preferences always tip the scales, so perfect balance never really occurs.
The puzzle has a modern echo in electronics. A digital circuit that must decide between 0 and 1 from an input that is neither can linger in an undecided 'metastable' state. If it hesitates longer than the system's clock allows, errors follow. Sometimes the best decision is simply to make one.
Source: Wikipedia — Buridan's ass · Text summarised from Wikipedia (CC BY-SA 4.0)
