Contrary to the rather commonly held opinion that the understanding of prudence (as a certain virtue) has not changed essentially since the ancient times, it is argued in the paper that there are two not only distinct but also incompatible concepts of prudence: the modern – amoral or nonmoral, and the classical (Aristotelian-Th omist) – strictly moral. Th e claim that these concepts are distinct and incompatible implies that ‘modern prudence’ is not part of ‘classical prudence’ but is essentially diff erent from it: one cannot be prudent in both senses (for instance, part of modern prudence is continence/self-control, whereas classical prudence excludes continence/self-control). Apart from the comparison of both concepts of prudence, the paper also provides an analysis of their relations with the so-called ‘prudential values’ as well as of the causes of the evolution (or rather: revolution) in the understanding of prudence which took place in modern philosophy; It is also argued that within ethics which assumes the classical understanding of prudence there is no place for what Sidgwick called the ‘dualism of practical reason’.