Conjoined twinning is said to show that the number of human people—the number of us—can differ from the number of human organisms, and hence that we are not organisms. The paper shows that these arguments either assume the point at issue, rely on dubious and undefended assumptions, or add nothing to more familiar arguments for the same conclusion.

We can start with some science fiction. Here on Earth, I enter the Teletransporter. When I press some button, a machine destroys my body, while recording the exact states of all my cells. This information is sent by radio to Mars, where another machine makes, out of organic materials, a perfect copy of my body. The person who wakes up on Mars seems to remember living my life up to the moment when I pressed the button, and is in every (...) other way just like me. (shrink)

This paper is about the neglected question of what sort of things we are metaphysically speaking. It is different from the mind-body problem and from familiar questions of personal identity. After explaining what the question means and how it differs from others, the paper tries to show how difficult it is to give a satisfying answer.

We defend the view that we are not identical to organisms against the objection that it implies that there are two subjects of every conscious state one experiences: oneself and one’s organism. We then criticize animalism —the view that each of us is identical to a human organism—by showing that it has unacceptable implications for a range of actual and hypothetical cases of conjoined twinning : dicephalus, craniopagus parasiticus, and cephalopagus.

Animalism is the view that you and I are animals. That is, we are animals in the straightforward sense of having the property of being an animal, or in that each of us is identical to an animal-not merely in the derivative sense of having animal bodies, or of being "constituted by" animals. And by 'animal' I mean an organism of the animal kingdom." Sensible though it may appear, animalism is highly contentious. The most common objection is that it conflicts (...) with widespread and deep beliefs about our identity over time. These beliefs are brought out in reactions to fictional cases. Suppose, for instance, that your brain is transplanted into my head. The being who ends up with that organ, everyone assumes, will remember your life and not mine. More generally, he will have your beliefs, preferences, plans, and other mental properties, for the most part at least. Who would he be-you, me, or someone else? (shrink)