The debate on personal identity has profoundly modified the approach to the analysis of
prudence, its structure and its links with rationality and morality. While in ethics of 18th
and 19th centuries the problem of justifying prudent behaviour rationally did not exist,
in contemporary ethics it seems no longer possible to justify it rationally. Particularly,
from the perspective of the complex account of personal identity it seems that the only
way to condemn great imprudence is from the point of view of morality. In this way we
assist to a slow erosion of the clear-cut distinction between prudence and morality. The
paper illustrates this change contrasting the analysis of prudence made by Joseph Butler,
and then followed by his heir Henry Sidgwick, with that recently made by Derek
Parfit.
