Key Arguments

• He notes that if his mother had conceived within a few days of when she actually conceived him, the child could have grown from the same ovum but 'almost certain[ly]' from a different spermatozoon, thus sharing some but not all of his genes.
• He claims that in such a case we are 'inclined to believe that any question about our identity must have an answer, which must be either Yes or No', but he rejects this and maintains that 'There are cases in which our identity is indeterminate.'
• He proposes that in the described near‑conception case 'my question has no answer. It is neither true nor false that, if these events had occurred, I would never have existed. Though I can always ask, ‘Would I have existed?’, this would here be an empty question.'
• Because these indeterminacy claims are controversial, and he wants the Time‑Dependence Claim to be uncontroversial, he 'set[s] aside these cases' and introduces a weaker, time‑buffered version: '(TD2) If any particular person had not been conceived within a month of the time when he was in fact conceived, he would in fact never have existed.'
• He emphasizes that he only claims TD2 is 'in fact true', not that it is 'necessarily true', in order to avoid disputes about metaphysical modality and restrict attention to what would in fact have happened.

Source Quotes

Each of us grew from a particular pair of cells: an ovum and the spermatozoon by which, out of millions, it was fertilized. Suppose that my mother had not conceived a child at the time when in fact she conceived me. And suppose that she had conceived a child within a few days of this time. This child would have grown from the same particular ovum from which I grew.

This child would have grown from the same particular ovum from which I grew. But even if this child had been conceived only a few seconds earlier or later, it is almost certain that he would have grown from a different spermatozoon. This child would have had some but not all of my genes. Would this child have been me?

We are inclined to believe that any question about our identity must have an answer, which must be either Yes or No. As before, I reject this view. There are cases in which our identity is indeterminate. What I have just described may be such a case. If it is, my question has no answer.

If it is, my question has no answer. It is neither true nor false that, if these events had occurred, I would never have existed. Though I can always ask, ‘Would I have existed?’, this would here be an empty question. These last claims are controversial.

Since I want my Time-Dependence Claim not to be controversial, I shall set aside these cases. The claim can become (TD2) If any particular person had not been conceived within a month of the time when he was in fact conceived, he would in fact never have existed. I claim that this is in fact true.

Key Concepts

• Suppose that my mother had not conceived a child at the time when in fact she conceived me. And suppose that she had conceived a child within a few days of this time.
• even if this child had been conceived only a few seconds earlier or later, it is almost certain that he would have grown from a different spermatozoon. This child would have had some but not all of my genes.
• There are cases in which our identity is indeterminate. What I have just described may be such a case.
• It is neither true nor false that, if these events had occurred, I would never have existed. Though I can always ask, ‘Would I have existed?’, this would here be an empty question.
• (TD2) If any particular person had not been conceived within a month of the time when he was in fact conceived, he would in fact never have existed.

Context

Early in Section 119, Parfit discusses borderline conception‑time cases to motivate a more cautious, one‑month version of the Time‑Dependence Claim (TD2) that avoids controversial issues about identity indeterminacy.