You are feeling extremely lucky. You have just been approached by an eccentric
billionaire who has offered you the following deal. He places before you a vial of toxin that, if
you drink it, will make you painfully ill for a day, but will not threaten your life or
have any lasting effects. (Your spouse,
a crack biochemist, confirms the properties of the toxin.) The billionaire will pay you one million
dollars tomorrow morning if, at midnight tonight, you intend to drink the
toxin tomorrow afternoon. He emphasizes
that you need not drink the toxin to receive the money; in fact, the money will
already be in your bank account hours before the time for drinking it arrives,
if you succeed. (This is confirmed by
your daughter, a lawyer, after she examines the legal and financial documents
that the billionaire has signed.) All
you have to do is sign the agreement and then intend at midnight tonight to
drink the stuff tomorrow afternoon. You
are perfectly free to change your mind after receiving the money and not drink
the toxin. (The presence or absence of
the intention is to be determined by the latest ‘mind-reading’ brain scanner
and computing device designed by the great Doctor X. As a cognitive scientist, materialist, and
faithful former student of Doctor X, you have no doubt that the machine will
correctly detect the presence or absence of the relevant intention.)

Thus begins Gregory Kavka’s short classic, “The Toxin Puzzle” (Analysis 43 (1983): 33-36).

Suppose you could really use one million dollars. Well, come to think of it, we should perhaps start
raising that amount in retellings of Kavka’s puzzle to account for inflation –
to avoid a Dr. Evil-style embarrassment
down the line–though I could still really use a paltry million dollars! So, let’s say this is an eccentric multi-billionaire
whose offer is for $10 million. That
should let the example keep its punch for quite a number of years into the
future. So, you can really use $10
million, and if the offer was simply to get that money if you drink the toxin,
you would happily do it. Now, you might
think the offer being made to you is even better than a simple payment for
drinking the toxin, because, the way it’s set up, you can have your cake and,
well, avoid puking it up, too: You can intend to drink the toxin at midnight
tonight, pocket the money, and then change your mind and never drink the toxin. But as they think it over, most people start
to realize things might not be that simple. If you’ll know full well at midnight that you will have no reason at all
to drink the toxin tomorrow afternoon – by then, you’ll either have the money
or you won’t, and, either way, drinking the toxin will simply make you sick
while providing no financial benefit – well, then, maybe pocketing the money
might not be so easy. (Oh, that fiendish
billionaire!) The question to ponder is:
Given that set-up…

Can you form the intention?

Kavka realizes that there are some gimmicky ways of coming to have
the intention, and rules these ways out:

At this point, your son, a strategist for the Pentagon,
makes a useful suggestion.  Why not bind
yourself to drink the stuff tomorrow, by today making irreversible arrangements
that will give you sufficient independent incentive to drink it?  You might promise someone who would not later
release you from the promise that you will drink the toxin tomorrow
afternoon.  Or you could sign a legal
agreement obligating you to donate all your financial assets (including the
million if you win it) to your least favourite political party, if you do not
drink it.  You might even hire a hitman
to kill you if you do not swallow the toxin. 
This would assure you of a day of misery, but also of becoming
rich.  Unfortunately, your daughter the
lawyer, who has read the contract carefully, points out that arrangement of
such external incentives is ruled out, as are such alternative gimmicks as hiring a
hypnotist to implant the intention, forgetting the main relevant facts of the
situation, and so forth.

Oh, that fiendish billionaire!  If I’m understanding that “and so forth”
correctly, the question we’re left with is: If you really want that $10
million, can you, just by an act of the will, summon up the intention to drink
the toxin, while fully realizing that when the time comes to drink it, you will have
absolutely no reason to do so, and a fairly strong reason not to?  For now, I just leave that as a question for
you to ponder…