The cool nifty thing that totally made my day was finally getting around to learning the "print" command in gdb. It seems so stupid in retrospect to have been using compiled print statements all these years when I could have examined any variable interactively with a simple debug flag. Now if only gdb could step backwards...

In "Free Will - Even for Robots", John McCarthy describes what he feels are the minimal criteria for a complex system to be considered as possessing free will, namely the ability to state "I can, but I won't".

The decision process of such an entity is divided into two phases, starting with the consideration of all possible actions, i.e. what it can do, and then further searching within that set for what it wants most to do.This manner of breaking down the problem of choice is simply a strategy for building good adaptive goal-seeking systems. It is a strategy that works best when considerations of what can be done and what is wanted are well separated, either in terms of possible perturbations (factors mostly affecting one thing or another) or in terms of time-scale (can possibly changing faster than want). By exploiting this natural factoring, goal-seeking systems are able to adapt faster/more efficiently to changing/different conditions. On top of being structured internally like this, people also try to predict each other's actions by assessing ability (can) and intent (want) separately. Again, it makes sense to do so because the inference and knowledge used to estimate the two vary greatly.

Incompatabilists, of which there are quite a few, hold that free will and determinism are in conflict. These are the people who drag Quantum Mechanics into the discussion. I find determinism to be irrelevant to the issue of free will - a person deciding to do something by flipping a coin does not seem any freer to me. The issue here is that of subjective uncertainty - when flipping a coin, not even the person knows what's going to happen next, and hence that uncertainty is shared amongst all the agents, making it objective. A person with free will is one whose actions are unpredictable to others and yet can in retrospect be proven to have been fully decided on by the person internally. The question is, how does one furnish such a proof?

Thanks to some very good points made by wakaba I've decided to write a followup post.

More cash is always worth more than less cash. Rationally trading two differing amounts of the same currency is thus impossible. A stock has risk; its future dividend is not guaranteed. Estimating the value of a stock involves constructing a probability distribution for the future stock dividends.

Different people have different information, and may thus infer different distributions. However, even when they have the same beliefs and infer the same distribution, they will still price the stock differently depending on their differing appetites for risk. For example, a grad student would be willing to pay less than a millionaire for the same 50% chance at winning $10,000. See also the St Petersburg Paradox.

A corollary of this line of logic: given that two people infer the same probability distribution A, they will arrive at the same price for the stock as the uncertainty of A becomes smaller and the appetite for risk becomes irrelevant.