Reductionism means that “Jones” and “Smith” are not platonic concepts. They’re made out of parts, and you can look at the parts and ask how they contribute to moral responsibility.
When you say “Smith has a brain tumor that made him do it”, you are conceiving of Smith and the brain tumor as different parts, and concluding that the non-tumor part isn’t responsible. If you ask “Is the Smith-and-brain-tumor system responsible for the murder”, the answer is yes. If you break the mind of Jones into parts, you could similarly ask “Is the visual cortex of Jones responsible for the murder”, and the answer would be no.
So, why do we conceive of “Smith” and “the brain tumor” as more naturally separable? Because we have an understanding that the person Smith was before the brain tumor has continuity with the current Smith+brain tumor system, that the brain tumor is separable using surgery, that the post-surgery Smith would have continuity with the current Smith+brain tumor system, that the post-surgery Smith would approve of the removal of the brain tumor, and the pre-tumor Smith would approve of the removal of the brain tumor.
Whereas we don’t have an understanding of Jones in that way. If we did, maybe if we were visited by aliens which had much more advanced neuroscience, and they pointed out that lead exposure had changed a neural circuit so that it operated at 85% efficiency instead of the normal 100%, and they could easily change that, and the post-change Jones didn’t want to commit any murders, we might not consider the new Jones morally responsible. But the old Jones-minus-efficiency was responsible.
Reductionism means that “Jones” and “Smith” are not platonic concepts. They’re made out of parts, and you can look at the parts and ask how they contribute to moral responsibility.
When you say “Smith has a brain tumor that made him do it”, you are conceiving of Smith and the brain tumor as different parts, and concluding that the non-tumor part isn’t responsible. If you ask “Is the Smith-and-brain-tumor system responsible for the murder”, the answer is yes. If you break the mind of Jones into parts, you could similarly ask “Is the visual cortex of Jones responsible for the murder”, and the answer would be no.
So, why do we conceive of “Smith” and “the brain tumor” as more naturally separable? Because we have an understanding that the person Smith was before the brain tumor has continuity with the current Smith+brain tumor system, that the brain tumor is separable using surgery, that the post-surgery Smith would have continuity with the current Smith+brain tumor system, that the post-surgery Smith would approve of the removal of the brain tumor, and the pre-tumor Smith would approve of the removal of the brain tumor.
Whereas we don’t have an understanding of Jones in that way. If we did, maybe if we were visited by aliens which had much more advanced neuroscience, and they pointed out that lead exposure had changed a neural circuit so that it operated at 85% efficiency instead of the normal 100%, and they could easily change that, and the post-change Jones didn’t want to commit any murders, we might not consider the new Jones morally responsible. But the old Jones-minus-efficiency was responsible.