Kavka's toxin puzzle is a thought experiment about the possibility of forming an intention to perform an act which, following from reason, is an action one would not actually perform. It was presented by moral and political philosopher Gregory S. Kavka in The Toxin Puzzle (1983), and grew out of his work in deterrence theory and mutual assured destruction.
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The puzzle
Kavka's original version (as cited in [1]):
He places before me a vial of toxin that, if I drink it, will make me painfully ill for a day, but will not threaten my life or have any lasting effects. . . . The billionaire will pay me one million dollars tomorrow morning if, at midnight tonight, I intend to drink the toxin tomorrow afternoon. He emphasizes that I need not drink the toxin to receive the money; in fact, the money will already be in my bank account hours before the time for drinking it arrives, if I succeed. . . . All I have to do is . . . intend at midnight tonight to drink the stuff tomorrow afternoon. I am perfectly free to change my mind after receiving the money and not drink the toxin.
A possible interpretation: Can you intend to drink the toxin, if you know you don't have to?
The paradox
The paradoxical nature can be stated in many ways, which may be useful for understanding analysis proposed by philosophers:
- In line with Newcomb's paradox, an omniscient pay-off mechanism makes a person's decision known to him before he makes the decision, but it is also assumed that the person may change his decision afterwards, of free will.
- Similarly in line with Newcomb's paradox; Kavka's claim, that one cannot intend what one will not do, makes pay-off mechanism an example of reverse causation.
- Pay-off for decision to drink the poison is ambiguous.
- There are two decisions for one event with different pay-offs.
Since the pain caused by the poison would be more than off-set by the money received, we can sketch the pay-off table as follows.
| Intend | Do not intend | |
|---|---|---|
| Drink | 90 | -10 |
| Do not drink | 100 | 0 |
According to Kavka: Whether you are paid or not, drinking the poison would leave you worse off. A rational person would know he would not drink the poison and thus could not intend to drink it.
| Intend | Do not intend | |
|---|---|---|
| Drink | Impossible | -10 |
| Do not drink | Impossible | 0 |
David Gauthier argues once a person intends drinking the poison one cannot entertain ideas of not drinking it.[2]
The rational outcome of your deliberation tomorrow morning is the action that will be part of your life going as well as possible, subject to the constraint that it be compatible with your commitment-in this case, compatible with the sincere intention that you form today to drink the toxin. And so the rational action is to drink the toxin.
| Intend | Do not intend | |
|---|---|---|
| Drink | 90 | -10 |
| Do not drink | Impossible | 0 |
Now, we need to consider whether or not it is possible to form an intention to perform a future act, given the foreknowledge that after forming the intention you will have no incentive to fulfill your intention. In fact, a person X who attempts this will have very good reasons not to. As soon as X intends to drink the toxin, X can collect the reward—X does not actually have to drink it. So, once the time has come to drink the toxin, the reward will already have been collected and the only thing that will result from drinking the toxin will be extreme discomfort—having received the reward, no incentive remains to drink the toxin. Given this foreknowledge, it seems unreasonable for X to drink the toxin. But considering that X already has this information and can come to this conclusion, then it seems unlikely that X would be able to intend to drink the toxin.
See also
References
- ^ Eggleston, Ben The Toxin and the Tyrant: Two Tests for Gauthier’s Theory of Rationality
- ^ Gauthier, David: "Assure and Threaten", Ethics, Vol. 104, No. 4. (Jul., 1994), pp. 690-721.
