It seems to me that free will can be easily tested. The next time someone is getting brain surgery, just take a few minutes to perform the test. Sometimes the patient remains awake during brain surgery so he can report what functions are changing as the surgeon is poking around. So for example, when the surgeon electrically stimulates the language center of the brain, the patient might temporarily lose his ability to speak.
The test for free will would be this, for example: First the doctor locates the place in the brain where electrical stimulation causes the patient to lose speech. Then the surgeon asks the patient to keep speaking normally despite the electrical stimulation.
If the patient can speak normally despite having the speech center stimulated, then the patient has free will that can overcome the normal chain of cause and effect in the brain. If he can’t speak, then you have proven the brain is nothing but a moist and complicated machine and your life is a pointless series of miseries.
Maybe there’s a reason no one is testing for free will.
I know Adams meant this experimental proposal in jest, but it’s still worth taking a moment to disagree with it. First of all, no sane person doesn’t believe that our free will is bounded in some very significant ways. I want to fly, and be a rock star, and be as funny as Dilbert, but, as another rock star once sang, you can’t always get what you want.
Once we give up the absurd notion of perfect freedom, we realize that our freedom is a sliding scale. Our will might be bounded by all sorts of practical constraints, but that doesn’t mean it doesn’t exist. (Daniel Dennett takes a similar position in his book Freedom Evolves, which argues that freedom has been steadily increasing via biological evolution.)
Now back to Adams’s thought experiment. Nobody really believes that, if your language brain areas were excised, you could miraculously keep on talking. The same is true for the visual cortex, the motor areas, and just about any other fold of the brain. Once your machine is broken, your ghost can’t save you. (Of course, as I mentioned earlier, the possibility of neural plasticity means that your machine can also sometimes fix itself.)
But all Adams’s thought experiment has proven is that our free will isn’t absolute. Because our being depends upon our material brain – this is one of our many constraints – if that brain is injured, then so are we. Our freedom has been taken from us.
My point is that we shouldn’t use these extreme examples of material causality – such as having a massive tumor in your frontal cortex, or getting your language areas cut out – to make general claims about the brain and free will. All they do is disprove a definition of freedom that nobody actually believes in. (Unless, of course, you are a Cartesian dualist, and don’t believe that that the mind has much to do with the brain.)