Key Arguments

• Parfit explicitly states the weaker conclusion: 'On the weaker of my two conclusions, when S and P conflict, it would be rational to follow either.'
• He notes that, under this conclusion, 'S would have lost its claim to be the one true—or best—theory.'
• S loses its bolder principle (S12): 'It would have lost the bolder claim (S12) It is irrational to act, knowingly, against one’s own self-interest merely to achieve what, at the time of acting, and after ideal deliberation, one most wants or values.'
• S retains only the weaker (S13): 'It would be left with (S13) It is rational to act, knowingly, in one’s own self-interest, even when one knows that this will frustrate what, after ideal deliberation, one most wants or values.'
• Symmetrically, P fails to secure its own bolder claim (P11) and keeps only the weaker (P12): 'The Present-aim Theory would not have won the bolder claim (P11) It is irrational to act in one’s own self-interest when one knows that this will frustrate what, after ideal deliberation, one most wants or values. It would have won only (PI2) It is rational to do what one knows will best achieve what, after ideal deliberation, one most wants or values, even when one knows that this is against one’s own self-interest.'
• Parfit emphasizes that despite this formal symmetry, the loss bites harder for S because 'It is more important for S to make the bolder of its claims. In losing (SI3) it has lost what it needs in its conflict with P. It is not enough to have kept the weaker (S12).'

Source Quotes

B HOW MY WEAKER CONCLUSION WOULD IN PRACTICE DEFEAT S On the weaker of my two conclusions, when S and P conflict, it would be rational to follow either. This conclusion would be highly damaging to the Self-interest Theory.

Formally, the result would be symmetrical. S would have lost its claim to be the one true—or best—theory. It would have lost the bolder claim (S12) It is irrational to act, knowingly, against one’s own self-interest merely to achieve what, at the time of acting, and after ideal deliberation, one most wants or values.

S would have lost its claim to be the one true—or best—theory. It would have lost the bolder claim (S12) It is irrational to act, knowingly, against one’s own self-interest merely to achieve what, at the time of acting, and after ideal deliberation, one most wants or values. It would be left with (S13) It is rational to act, knowingly, in one’s own self-interest, even when one knows that this will frustrate what, after ideal deliberation, one most wants or values.

It would have lost the bolder claim (S12) It is irrational to act, knowingly, against one’s own self-interest merely to achieve what, at the time of acting, and after ideal deliberation, one most wants or values. It would be left with (S13) It is rational to act, knowingly, in one’s own self-interest, even when one knows that this will frustrate what, after ideal deliberation, one most wants or values. The Present-aim Theory would not have won the bolder claim (P11) It is irrational to act in one’s own self-interest when one knows that this will frustrate what, after ideal deliberation, one most wants or values.

It would be left with (S13) It is rational to act, knowingly, in one’s own self-interest, even when one knows that this will frustrate what, after ideal deliberation, one most wants or values. The Present-aim Theory would not have won the bolder claim (P11) It is irrational to act in one’s own self-interest when one knows that this will frustrate what, after ideal deliberation, one most wants or values. It would have won only (PI2) It is rational to do what one knows will best achieve what, after ideal deliberation, one most wants or values, even when one knows that this is against one’s own self-interest. But, though there is formal symmetry, the comparable claims have for these two theories different importance.

It would have won only (PI2) It is rational to do what one knows will best achieve what, after ideal deliberation, one most wants or values, even when one knows that this is against one’s own self-interest. But, though there is formal symmetry, the comparable claims have for these two theories different importance. It is more important for S to make the bolder of its claims. In losing (SI3) it has lost what it needs in its conflict with P. It is not enough to have kept the weaker (S12). Before I defend this claim, I shall consider a similar claim about the conflict between S and morality.

Key Concepts

• On the weaker of my two conclusions, when S and P conflict, it would be rational to follow either.
• S would have lost its claim to be the one true—or best—theory.
• It would have lost the bolder claim (S12) It is irrational to act, knowingly, against one’s own self-interest merely to achieve what, at the time of acting, and after ideal deliberation, one most wants or values.
• It would be left with (S13) It is rational to act, knowingly, in one’s own self-interest, even when one knows that this will frustrate what, after ideal deliberation, one most wants or values.
• The Present-aim Theory would not have won the bolder claim (P11) It is irrational to act in one’s own self-interest when one knows that this will frustrate what, after ideal deliberation, one most wants or values. It would have won only (PI2) It is rational to do what one knows will best achieve what, after ideal deliberation, one most wants or values, even when one knows that this is against one’s own self-interest.
• But, though there is formal symmetry, the comparable claims have for these two theories different importance. It is more important for S to make the bolder of its claims. In losing (SI3) it has lost what it needs in its conflict with P. It is not enough to have kept the weaker (S12).

Context

Opening of Appendix B ('HOW MY WEAKER CONCLUSION WOULD IN PRACTICE DEFEAT S'), where Parfit restates his weaker conclusion about the rational status of S and P, spells out which specific principles each theory loses or retains, and notes the formal symmetry yet asymmetric practical significance of these losses.