This truly stimulating work in all its approach is a complete and clear treatise on the foundations of the modern theory of morality. Your reflections on normative ethics - moral principle that you recommend? They offer a new approach to a long-neglected issue. First, the author deals with the status of ethics and defends the position that there are no objective values, ie that morality is not an existing field and only to discover, but must be built continuously. Next, it analyzes the contents of ethics and defines morality as a functional mechanism that is practically the same over time, but that changes in its significance according to the evolution of the human condition. Mackie outlines a system of practical morals, for which he borrows a series of elements from the utilitarian and absolutist orientations, which he previously critically reviews in some of its implications. Third, the author explores the limits and intersections between ethics, psychology, metaphysics, theology, law and politics. The purpose throughout this work is the discussion of a wide range of philosophical issues and practical morals, which moves within a differentiated version of subjectivism and that can be defined as a theory of the "error" of the apparent objectivity of the values. The references of this discussion are the most outstanding contributions to ethics, from Plato and Aristotle to Hobbes, Hume, Kant and the most relevant contemporary positions. This classic of contemporary ethics, for the first time available in Spanish, has to become an essential reference text.