Ethics is the science of duty, i.e. the science that elucidates the rules of the right behavior. Nevertheless, it seems that the way we rule our lives is intuitive and based on common sense. For instance, it is common to say that ethical rules are default rules, which means that they tolerate exceptions. Some authors argue that moral can only be grounded on particular cases while others defend the existence of general principles related to ethical rules. Our purpose here is not to justify the first or the second position, but to try to model ethical systems using artificial intelligence formalisms. More precisely, this is an attempt to show that progress in non-monotonic logics, which simulate common sense reasoning, provides a way to formalize different ethical conceptions. From a technical point of view, the model developed here makes use of the Answer Set Programming (ASP) formalism. It is applied to compare different ethical systems with respect to their attitude towards lying and could help to extend classical philosophy and to define general conditions required by any ethical system.