The principle of virtue corresponds to this initial choice: to be virtuous is to act with a view to obtaining one of them.
Bentham delineated four "sanctions" or sources of pain and pleasure, which he may have learnt from Gay's essay Concerning the Fundamental Principle of Virtue or Morality (1731): physical, political, moral, and religious.
Although he illustrates FUL and FEI in relation to maxims that he assumes to be obligatory or forbidden in the Groundwork, however, it is not until the Metaphysics of Morals that Kant argues systematically for duties by means of the CI and related principles, the universal principle of right (justice) and the supreme principle of virtue.
The principle of moral virtue is said to be a knowledge of what is helpful and what is damaging for survival and well-being in human society.
Kant does not claim to derive these duties from the CI or the supreme principles of right or virtue alone.
\(X\) understands, evaluates, and is capable of making modal claims, such as (iii) and (iv), because \(X\) has tacit knowledge of Principles of Possibility in virtue of which modal claims, such as (iii) and (iv), are understood, evaluated, and hold true.
The "supreme principle of the doctrine of virtue" is, "act in accordance with a maxim of ends that it can be a universal law for everyone to have" (MM 6 395).
As thisnesses are the formal principles in virtue of which individuals are what they are, something particular, concrete, and perfectly determined in itself, so these individual causal principles deriving from ideas are what causes the passage from the specific ideal standard to the analytical description of its instantiations (QdU, fol. 135ra).
He imagines the advent of "an age of leisure and abundance" in which his (hypothetical) grandchildren – now well into retirement – will be set free "to return to some of the most sure and certain principles of religion and traditional virtue, that avarice is a vice, that the exaction of usury is a misdemeanour, and the love of money is detestable".
