Imagine that Brian promises to drive you to the airport but never shows up, and you miss your flight. When you confront Brian, he tells you that he remembered his promise but decided to watch a movie instead. Would you be angry? You betcha!
But then suppose Brian pleads, “Don’t be angry at me. My brain made me do it. I wanted to watch the movie, and my desires are lodged in my brain. Moreover, I don’t care that much about you, but that is only because my neurons do not fire very fast when I think of you. My brain makes me act as I do, so I’m not responsible.” This plea will not quell your anger. Why not?
Brian is correct that his brain made him do it. It was not his legs or eyes that made him watch the movie. If his neurons had been wired differently, then he would have driven you as he promised. It also wasn’t the movie or another person that made him do it. It was his desires, which are in his brain (assuming that minds are not separate substances), so his brain is what caused him to do it.
Nonetheless, what really matters is which part of his brain made him do it. What made him let you down was activation levels in those parts of his brain that constitute Brian’s desires. That fact is just a pseudo-scientific way of saying that he did it because he wanted to. It doesn’t change when he re-describes his desires in terms of brain states.
What about mental illnesses? Addictions? Compulsions? Brainwashing? Hypnosis? Tumors? Coercion? Alien hand syndrome? Multiple personality disorder? These cases are all tricky, so philosophers disagree about which people in these conditions are responsible — and why. Nonetheless, these difficult cases do not show that there is no difference between seizures and normal desires, just as twilight does not show that there is no difference between night and day. It is hard to draw a line, but that does not mean that there is no line.
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