the bodily and brain criteria of personal identity, including their objections from teleportation and brain swaps

What this dot point is asking

VCAA wants you to explain the physical answers to the question of what makes a person at one time identical with a person at a later time: the bodily criterion and the brain criterion. You must distinguish numerical from qualitative identity, set out each criterion clearly, and evaluate them against thought experiments (brain transplants, teletransportation, fission) and against the rival psychological criterion. The high-band answer keeps the numerical/qualitative distinction sharp throughout and uses the transplant intuition to motivate the move from body to brain and then beyond.

Numerical versus qualitative identity

The first essential distinction. Qualitative identity is exact similarity: two new coins off the same press are qualitatively identical. Numerical identity is being one and the same thing: the coin in my left hand is numerically identical to the coin I had a moment ago, however it has changed. The problem of personal identity is about numerical identity: what makes the adult numerically the same person as the child, even though almost every cell, belief and feature has changed. A criterion of personal identity tells us the condition under which a person at time one is numerically identical to a person at time two.

The bodily criterion

The bodily criterion says: a person at a later time is identical to a person at an earlier time if and only if they have the same living human body, traced through continuous physical existence. This is attractively commonsensical. We re-identify people by their bodies every day, the criterion is public and checkable, it avoids any appeal to an unobservable soul, and it explains ordinary survival: you go on existing as long as your body does, even through sleep, coma or amnesia.

The brain criterion

The bodily criterion runs into a powerful intuition. Imagine your brain is transplanted into another body while your old body receives someone else's brain. Most people judge that you go with your brain: the person who wakes in the new body, with your memories and personality, is you, and your old body is now someone else. If that is right, identity follows the brain, not the body as a whole. The brain criterion therefore says: you are identical to the later person who has your brain (or the part of it that sustains your mental life), since the brain is the organ of the mind. This keeps the merits of physicalism while respecting the transplant intuition.

Evaluation

The brain-transplant case is the decisive objection to the simple bodily criterion. If we follow the person into the new body, then having the same whole body is not necessary for identity, and the bodily criterion is too crude. The bodily theorist can retreat to a narrower physical-continuity view (same brain, or same enough of it), which is just the brain criterion.

But the brain criterion faces its own pressure. Consider teletransportation: a machine records the exact state of every cell in your brain and body, destroys the original, and builds a perfect replica on Mars from new matter. The replica has all your memories and traits but not your original brain. Did you travel to Mars, or did you die and a duplicate now lives? The brain criterion must say you died, since your brain was destroyed, yet the replica seems to carry on your life seamlessly, which pulls intuition toward the view that psychological continuity, not the physical brain, is what matters.

The fission case (developed by Parfit) is sharper still. Suppose each half of your brain is transplanted into a different body, and both survive with your memories and character. Each resulting person is just as good a candidate to be you as in the ordinary transplant case. But they cannot both be you, since they are two people leading separate lives, and there is no non-arbitrary reason to pick one. The brain criterion, like any identity criterion, cannot handle this: identity is one-one, but the continuity that seems to matter has gone one-two. This is the central reason many philosophers conclude that what matters in survival is psychological continuity rather than strict numerical identity of a body or brain.

A further worry for any physical criterion is gradual replacement: if neurons were replaced one by one with functionally identical artificial parts, at no point would there be a clear loss of the person, yet eventually none of the original brain would remain. This again suggests the organising pattern matters more than the specific matter.

Judgement: the bodily criterion is the natural starting point but is refuted by the brain-transplant intuition, which we should follow our brains rather than our bodies. The brain criterion is a real improvement, capturing why we track the organ of thought. But teletransportation and especially fission show that even the brain criterion identifies the wrong thing: what we care about in survival is the continuation of our psychology, which can be duplicated or divided in ways numerical identity cannot follow. Physical criteria are therefore closer to common sense but ultimately less defensible than a psychological account, and fission suggests identity itself may not be what matters most.