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Michael Egnor: Philosopher’s claim that split brain surgery shows that we have no real identity is wrong

Derek Parfit at Harvard in 2015,
courtesy Anna Riedl (CC BY-SA 4.0)

Derek Parfit (1942-2017) was a highly esteemed philosopher who spent his career arguing that we have no true personal identity and he cited split-brain surgery as a thought experiment, showing why it couldn’t be true. What the real world situation?

Materialists like Derek Parfit cite split-brain surgery when they deny personal identity. I’ve done that operation so let me explain why they mislead us.

When a patient has had his cerebral hemispheres disconnected surgically (in order to treat epilepsy), nothing much happens. He is, by his own experience and in all normal activities of life, exactly the same as he was before his brain was cut in half. He is not in any sense “two people.” His identity is in no way altered or split.

Roger Sperry (1913–1994, pictured in 1981) was a neurophysiologist who understood the remarkable opportunity for neuroscience and philosophy of mind that patients with this surgery offered. He devoted much of his professional life to studying them. He too noted that in ordinary life they were completely normal.

By means of extensive and very clever experiments, he was able to discern perceptual differences after split-brain surgery. His results supported the standard theory that the right and left hemispheres of the brain subserve different perceptual and motor functions.

Michael Egnor, “Does split-brain surgery show that we have no real identity?” at Mind Matters News
Roger Sperry

But—despite what you might hear in Psych 1010—Sperry did not stumble on any kind of evidence for human beings not really having a personal identity. Quite the opposite.

You may also enjoy these articles by Michael Egnor on personal identity:

Interview with a woman (or women) formerly called Susan Blackmore: A professor of psychology argues that there is no continuity between our present selves and our past selves.

My right hemisphere is an atheist! No, wait… In reality, split-brain surgery does not split consciousness in any meaningful sense.

Yes, split brains are weird, but not the way you think. Scientists who dismiss consciousness and free will ignore the fact that the higher faculties of the mind cannot be split even by splitting the brain in half.

Also: Some people think and speak with only half a brain. A new study sheds light on how they do it.


Four researchers whose work sheds light on the reality of the mind The brain can be cut in half, but the intellect and will cannot, says Michael Egnor. The intellect and will are metaphysically simple.

Materialism is a failed worldview. Our identity is NOT our brain. Aristotle (and the soul) are Back. Truthfreedom

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