Joe at Oohlah's Blogspace recently mentioned Buridan's ass: caught between two equally-tempting piles of hay, the ass starves to death because it cannot choose between them. This is supposed to be a paradox. I may be missing something (as always, if I am then let me know!), but it strikes me as problematic only if we adopt an overly-abstract model of rationality. The supposed problem, I take it, is that absent any reason to prefer one option over another, it is irrational to choose either. The solution, I think, is to flesh out our abstractions with a little more practical detail.
Firstly, note that cognition comes at a cost - in terms of time, energy, and opportunity costs. So a rational agent should only cognize when the benefits of doing so outweigh these costs. Eventually one will reach a stage when further deliberation is no longer worth it, and one should engage in action instead. Thus grounding Buridan's Ass in an ecological context readily demonstrates its irrationality, for it continues to waste its resources assessing a choice that makes no difference.
Normally, once we realise that further deliberation is unproductive, we simply go ahead with our presently-favoured choice. The difficulty in this case is that, ex hypothesi, the ass has no favoured choice. One obvious solution would be to employ a random device, say, flip a coin. But I think even this is too much unnecessary effort. The ass should just pick one.
I think only a reasoner that had been abstracted away to the point of absurdity would find itself utterly 'frozen' in the situation of Buridan's ass. Any more realistic reasoner would be capable of making arbitrary decisions at ease (we certainly are!). Perhaps the sun shone more brightly on one side, or a bird was singing pleasantly to the other, or the agent was right-handed (hooved?). These are silly little things, of course, but any one would be enough to tip the scales and allow a decision to be made one way rather than the other.
Here one might complain that I have ignored the requirement that the agent (or ass) has no reason - not even a silly reason - to prefer one choice over the other. To this I would respond with a second appeal against abstraction, namely, to recognize that real-world cognition is a process in flux. Even if at one moment all its preferences perfectly balance out and the ass cannot choose one side over the other, we need only wait a moment for the next fluctuation to give rise to a slight imbalance.
The ass would not be constantly feeling exactly equal temptation for each pile of hay. That's just not how thinking works. Rather, the ass would be continually flickering back and forth in its preferences, as the equally-deserving bales of hay vied for its fickle favour. This more realistic view of cognition makes the problem disappear - for once our ass realises it's time to stop deliberating, it could simply go with whatever option happened to be favoured at that particular moment.
Update: Joe has more at Third Floor.