Experiment #35 · Thought experiment

Buridan's Ass

Can rational choice halt between equal options?

Attributed to Jean Buridan (14th c.); the example is older · c. 1340 · Free will, decision theory

First published: Discussed in Buridan's commentary on Aristotle's *De Caelo*; modern formulation in Spinoza, *Ethics* IIp49s.

A donkey equidistant from two identical bales of hay, dying of starvation because pure rationality cannot tip the scale.

A perfectly rational ass placed exactly equidistant from two identical bales of hay has, by hypothesis, no reason to prefer one to the other; the medieval worry was that it must therefore stand still and starve. The case is a thought experiment about determinism, free will, and the structure of practical reason: must equal reasons issue in equal inclinations, and if so what tips the balance? Spinoza, committed to a strict determinism, embraced the conclusion. Libertarians took it as a *reductio*. Modern decision theory reads it as showing the need for stochastic tie-breaking or "tiebreaker" agents distinct from pure rationality.

Formulation

Agent A; two options O₁ and O₂ with strictly identical expected value, no other distinguishing reason. Pure rationality is symmetric. Conclusion: agent is paralysed, unless some non-rational tiebreaker (caprice, randomness, volition) intervenes.

Compare this experiment

Dimensions Engaged

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Observer

Bears on Observer · Agency: is choice exhausted by reason, or does it include a non-rational component (will, caprice) that breaks ties?

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Time

Bears on Time · Freedom: a libertarian "free" choice in tie cases must come from somewhere; if not from reasons, then from a temporally local act of will.

Responses — How Schools Engage

Affirms / takes the bait 2

Determinism

If reasons are equal, the agent stands still — or, in any actual ass, microscopic asymmetries break the tie deterministically. There is no separate "will" to invoke; the case rules in determinism's favour.

Naturalism

Real biological agents are noisy; tie cases are resolved by stochastic neural processes. The thought experiment dissolves once one drops the idealisation of perfect rationality.

Denies / rejects the premise 1

Rationalism

Genuine reasons rarely tie at the level of resolution that matters; the case is artificial. Where ties do occur, indifference and arbitrary selection are themselves rational.

Reframes the question 3

Existentialism

A vindication of the priority of choice over reason: the agent must simply choose, and the choice creates the value rather than tracking it. Sartre's "radical choice" is Buridan's answer.

Pragmatism

Practical rationality includes the disposition to pick *something* rather than nothing in tie cases; a tiebreaker is not a defect of rationality but part of what it is to be a deliberating agent.

Occasionalism

For a Malebranchean, all motion is direct divine action; the ass moves because God wills it to, not because either bale outweighs the other. The puzzle depends on a naturalistic causal premise that occasionalism does not grant.