The philosophical work of Iris Murdoch, although not so extensive, cannot be easily grasped through usual classifications. Here we suggest approaching it from the perspective of Moore's thesis on the indefinable nature of good that she endorsed after having reexamined it. This comparison with Moore, however, is part of a more general and deeper investigation on the platonic Idea of the Good itself. Thus, after having analyzed how Murdoch understood and assessed the transition from Moore's conception to the contemporary framework shared by emotivism and R. Hare's prescriptivism, we clarify the idea of the sovereignty of good by emphasizing the following three aspects: the link between the realm of good and the authority of truth; the unifying power of the idea of good, in regard to reality as we experience it in our lives; lastly, the way in which this idea enables us to transcend the limits of our inherited theoretical horizons, thus revealing the true nature of human freedom.
