Tuesday, May 19, 2009

Mental/Physical Causation.

Imagine David Hume is thirsty, and decides that an India Pale Ale will do just right. Pursuant to that desire, he gets up from his computer, walks across to his kitchen, opens the fridge, extracts a pint of IPA, opens it and drinks. (This, only after he worries about the break in concentration this may cause. He deliberates, then moves)

If you were to ask him what just happened he'd say something we can represent with the simple flow-chart on the bottom portion of the slide (Click the slide to see a higher resolution version, then hit your 'back' button to return). After some indecision and deliberating, he decided to get the IPA and did.

Suppose that some neurologist was also at the same time 'observing' Dave by way of an elaborate room sized magnetic imaging device he had created. Imagine the device is exquistely sensitive and quite capable of picking up the electrochemical activity of Dave's brain, nervous system and musculature, rendering a highly detailed 3D image.

Ask this guy 'what just happened?'

How will he answer? His answer will be more like the top portion of the slide.

What is more; he'll say something like the following:

"Look, given the chemical states in the synapses and the voltage potential of the individual neurons in the system as these were at the beginning of the process (that is; at that initial brain state to the left) I can see that the 'cascade' of neural events that terminated in the muscle movements were bound to happen, determined by the chemistry and physics involved. Things had to happen that way. In fact, I could have predicted Dave's movements if I so chose."

Dave doesn't believe this. Neither do you. You both challenge him to predict Dave's next move. Dave does not tell you what he will do. He thinks he'll be clever by jumping out the window (he's on the ground floor. Never fear)

The neuroscientist pulls out his slide-rule (he's old school). He fiddles with it a bit, and writes his prediction, and sets it face down on the table. "Ok," he says, "I'm ready."

Dave devilishly grins, runs and jumps out the window landing safely in his front yard next to the gnome, laughing and pointing at the neuroscientist.

You move to the table, turn over the prediction. To a tee it describes what you just saw.

The neuroscientist just nods.

Dave thinks he freely chose to drink the IPA and equally freely chose to jump out the window to confound the neuoroscientist.

The neuroscientist was correct in his prediction. Things did unfold as he predicted. He insists Dave was bound to do the two things he did, and that this was determined by earlier states of his brain, in conjunction with some natural laws.

Who is right? Can both be right?