Tuesday, October 06, 2009

An Argument Against Libertarian Free Will

Suppose I am deciding whether or not to buy ice cream. Suppose also that all things being equal, a past-omniscient agent would predict a 50/50 chance of my buying ice cream. How does my final decision get made? Is there a reason for it?

Before I go any further, I want to note that I'm not talking about probabilities that result from a lack of knowledge on our part. If I flip a coin, I typically estimate the odds of tails at 50%, but that's really due to my ignorance about the behavior of a coin when I flip it. However, an observer who is omniscient about the past will be able to predict the outcome of my coin flip by computing what the laws of physics have to say about forces on the coin. In other words, when I speak of probabilities below, I'm talking about probabilities as they appear to an observer who is omniscient about the past.

According to libertarians, I somehow choose to buy or not buy the ice cream without my decision being (1) fully determined by the past, (2) random, or (3) some combination of determined and random.

Let's suppose that the world is not fully deterministic. How can the outcome of an event be partially determined?

Well, in quantum mechanics, as an example, the probability distribution for the event outcomes is determined, but the actual outcome is the result of a random selection according to the distribution.

For example, suppose a quantum theory predicts a 67% chance of an experiment finding an electron spin-up versus a 33% chance of finding the electron spin down. The theory says that nature acts as if the experiment is equivalent to placing 67 red balls and 33 green balls in a barrel, and randomly drawing a ball from the barrel. If the ball comes up red, then the electron is spin up, otherwise it is spin down. The past-omniscient observer only knows how many of each type of ball there are in the barrel.

This way of looking at events is quite general. It's not general because the world is physical, material or made up of quantum elements. It's general in the theoretical sense. If the past is determining something, then the past is altering the probability that an outcome will occur. A fully deterministic world is one in which the probabilities of outcomes are either 0% or 100%.

When pushed, even libertarians will agree that the past makes certain outcomes more probable than others. Will I choose to step in front of a moving bus this afternoon? Being a happy, stable person who lives a charmed life, probably not. Indeed, very probably not. Even if the libertarian believes I have the "free choice" to step in front of a moving bus, they can still admit that that choice is highly improbably due to factors in my past.

However, when we factor out the probability, what is left for a decision to be based upon?

It's very frustrating trying to pin down incompatibilists on this issue. As far as I can tell, the incompatibilist's belief in libertarian free will is generated by moral considerations, and comes without any technical accounting. For most libertarians, there is not only no mechanism for free will, but there's no way of distinguishing free will from randomness.

To make my argument more airtight, I'm going to suppose there's a detailed accounting for deterministic factors. What we'll see is that there's no basis for an agent to make a choice except via fundamental randomness.

Suppose I enumerate all the reasons I have to buy ice cream, and all the reasons not to buy ice cream. Suppose there turn out to be 5 reasons to buy (B1, B2, ..., B5), and 5 reasons not to buy (N1, N2, ..., N5).

For example, perhaps

N2 = "Ice cream will make me fat, and I want to be slim."

and

B4 = "Ice cream is one of the great pleasures of life, and I don't want to miss out on life's pleasures."

Each reason has an associated importance or weight. Being vain, I assign 10 points to N2, and 5 points to B4.

Since my vanity is is a part of my character, and my character is part of the past state of things, it is predictable. That is, the weight assigned to each reason is mostly determined by the past.

Suppose that these reasons and their weights translate into a 50/50 chance that I will buy the ice cream. That is, we are assuming that, all things being equal, the weight I assign to the reasons is such that they happen to cancel each other out.

At this stage of the thought experiment, the libertarian would say that I choose to buy or not to buy using my free will. What does this mean?

Well, something has to change the weighting of the reasons. It must be that, as I make my decision, I reassign weights to my reasons, and this causes me to come down on one side of the decision or the other.

But on what basis can I reassign weights to my reasons?

Presumably, the libertarian does not mean I am whimsical in reassigning the weights. Whimsy is random. There's no reason for it. It is arbitrary. To see this, imagine that my brain incorporates a random number generator which randomly shifts the weights of all the reasons. If the random number generator happens to throw the balance to buying the ice cream, I can't rationalize the decision by saying that my decision occurred because of B1-B5.

Could I have an actual reason to change my weights?

No. If I did have a reason to change weights such that I buy the ice cream, this reason would constitute B6, and should have been accounted for in my set. That is, the existence of such a reason contradicts the premise that I already had a complete set of reasons in sets B and N.

Is it possible that I discovered a new reason at the moment of my decision?

No. Nothing in the analysis above is phrased in terms of my own perspective. Rather, it's phrased in the perspective of a past-omniscient observer. It doesn't matter whether I was aware of B5. If I was unaware of it, the past-omniscient agent would have assigned it a low weight.

Is my attention to a particular reason the missing factor?

Well, attention or memory or prominence to consciousness may be a factor, but it doesn't help. Either there is a reason for the reason to have prominence to my consciousness or not. If there is a reason, it is already accounted for. If there isn't a reason, it is random.

At this stage, we are forced to conclude that whatever is not determined to the past-omniscient observer is fundamentally random. That is, there can be no possible reason or cause for the selection from the determined probabilities.

I would not be surprised to see some libertarians try to escape this conclusion by trying to redefine the word random. However, there's really nothing special to my definition. Just because an event occurs in the mind of an agent doesn't make any difference to my definition. There remains no reason for the decision, whether you call it random or not. Any attempt to make such a distinction is like saying that when a random event occurs in the mind of an agent, it's called whimsy. What value such nomenclature might have is beyond me.

8 comments:

Nevin ":-)" said...

Why is 50/50 so special? Even if your internal weightings resulted in, say, 60/40, something has to be random so that it doesn't degenerate into 100/0. Or am I missing something?

Also, the Libertarian could then watch you, and every time they determined the probability was 50/50, measure you and see if, in the long run, you buying ice cream was completely arbitrary.

Doctor Logic said...

Even if your internal weightings resulted in, say, 60/40, something has to be random so that it doesn't degenerate into 100/0. Or am I missing something?

No, you're quite correct. I could have used 60/40 as my starting point, but I thought 50/50 would be simpler.

Also, the Libertarian could then watch you, and every time they determined the probability was 50/50, measure you and see if, in the long run, you buying ice cream was completely arbitrary.

I'm not sure I understand your question. If the libertarian watches me, how will that help him? If my decision is not arbitrary, it must depend upon something. Being omniscient about the past, the libertarian would already have incorporated this dependency information into the analysis that gave them 50/50.

J said...

In regards to food, and other "basic needs," the determinist has solid arguments. Humans respond to impulses, sensations--say of hunger--and at best sort of direct those impulses: they seem to choose Taco Bell, instead of McBurgers. But of course they can't choose not to be hungry.

Perhaps that's compatibilism of a sort, but in a sense humans only say they can do differently. At lunch, they head over to Taco Bell--bio-chemical reality was so arranged to result in them heading to Taco Bell (one might . The "past omniscience" is sort of meaningless. They don't really know all the precise reasons, or "habit formation" in a sense, just like they couldn't describe their neurology in much detail. The same with say having to go to bathroom an hour later. Yes unsavory, but "the choice" is merely sort of guiding natural impulse.

Really the determinist wins, though there are problems with strict determinism in regards to higher thinking of humans. Say playing chess. You have to move, and you imagine, or "conceptualize" three or four moves in advance (or more if you are Karpov): it seems remarkably difficult to account for the ability to plot chess moves in advance via determinism-- certainly conceptual skills are unique to humans. I don't deny it could be deterministic, related to habit-formation, and skill, but in effect the bio-chemical mind does sort of "see the future", in a limited sense. So I would say I am 90% determinist, and 10% libertarian/compatibilist. The strict determinist has a long story to tell in regards to higher order thinking, mathematics, chess, logic, etc. Maybe an account can be given but ....formidable.


(Bricmont takes on these issues:
Bricmont Representin')

--Reppert is a blowhard.

Doctor Logic said...

J,

Thanks for the comment.

I agree that no one has "past omniscience", but I'm trying to make a point about what is possible in principle. My conclusion is that the world might be totally deterministic or partially deterministic, but if determinism is only partial, the complement of that determinism is fundamental randomness.

Also, when we talk of an agent as having the possibility of deciding differently, we really mean that, had the agent known something different, or felt differently, or preferred something different, then the agent could have decided differently. We don't mean that, given an identical situation with identical thoughts and feelings, the agent would have chosen differently.

IOW, the phenomenology of decision-making would be no different whether the universe was deterministic or determined + random.

it seems remarkably difficult to account for the ability to plot chess moves in advance via determinism

I don't see why this is difficult. I realize that we don't know all the mechanisms, but, in principle, it seems pretty straightforward. Chess players and allowed chess moves are deterministic. They are probabilistic, too, but that should not provide much of a computational challenge. Of course, humans don't usually brute force their computations, but think in terms of likely patterns instead. It just doesn't seem that mysterious to me.

J said...

Also, when we talk of an agent as having the possibility of deciding differently, we really mean that, had the agent known something different, or felt differently, or preferred something different, then the agent could have decided differently. We don't mean that, given an identical situation with identical thoughts and feelings, the agent would have chosen differently.


Well, she doesn't "have a possibility." She's hungry--so there is a biological impulse. She merely guides that. It's not substantially different than the old rat boxes, however trite; she has for years enjoyed tacos more than burgers (why, would be difficult to say). She believes, but does not know, one type of goal may be preferable; she might go for burgers tomorrow, but that doesn't necessarily mean she chose something different. It means her organism provided a different impulse.

So in effect her organism has developed a default setting for tacos! A bit strange, but in ways, behaviorist-determinist explanations do still apply to basic needs, like hunger.

(But you are mostly correct that some randomness neurologically speaking does not give her "free will" per se, though if randomness does occur before actions, it might be an issue for some actions--say the law, and crime, etc).

The behaviorist-determinist explanation doesn't apply in the same way to chess, however.
It may not be mysterious to us, as humans, or chess players, but obviously baboons don't play chess.

A chess game in effect shows that in some circumstances, bio-chemical matter sees ahead, has foresight--a concept. Thinking occurs. The behaviorists reduction does not suffice (except with a great deal of cog-sci, and brain science, that has not been worked out) Chess involves a modality--that is possibility, and contingency as well, as a Kantian might say--not merely stimulus/response, or cause/effect.

Does hamburger have concepts, or do amoebas, or even rats? Nyet. At least uniqueness. And in the case of chess, we can do differently. We can go back and pinpoint the exact move that went wrong, play the same opening again, and improve. The chess computer app. merely simulates human thinking--the chess rules
themselves a conceptual construct. Billiard ball physics simply does not apply to human brains and neurology.

May said...

No more posts?

backpacker said...

I've more of a "deterministic free will" opinion. Certainly there is no arbitrariness that jumps into the universe at the brain, nor are quantum effects an explanation for decision-making. The determinism is certainly there in the physics.

But the free will is in the human experience. I think that the inaccessibility of the outcomes of decisions beforehand means that we feel free will. For example, you will never be able to model a courtroom using the position and velocity of every atom, and physically predict the outcome of the court case.

Furthermore, there is no active agent forcing us to make decisions by coercion. And in the realm of human experience, that is called free will.

There's physics of particles, chemistry and biochemistry of molecules, cellular biological processes, etc, underlying human psychology and sociology. Free will is a useful description of human actions in the realm of psychology and sociology.

Doctor Logic said...

Apologies to backpacker that it took so long for your post to go up. Blogger added comment moderation while I wasn't looking.