Abstract: In "Rational Altruism" principles of morals are developed and rationally justified with strong emphasis on this justification. Therefore, the proper ethics is based on a prudentialist desirability theory, which in turn is based on an empirial theory of action. The theory of action particularly explores how decisions can be influenced by information and which types and principles of decision remain stable when the subject is confronted with new information. The prudentialist desirability theory on the basis of these empirical findings defines criteria for 'desirability' which among others should be stable in confrontation with new information, thus beating the rationality standards of utility theory. In the ethical part, finally, a criterion for distributive justice, called "utilex", is developed from the empathy based part of the prudentialist desirability function. Utilex is a prioritarian synthesis of utilitarianism and leximin; like our empathy it is biased towards the worse off without giving them an indefinitely high priority.