The question of "what is a self" is probably the most puzzling and persistent in philosophy. It announces itself with the Oracle at Delphi's injunction: "know thyself." Such an injunction, of course, presupposes that there is something there to be known, that the self can stand there as an object of knowledge, that the knower can know himself. Knowing himself, he can know himself as knower. This means that he can grasp the very performance which is himself as knower, is himself as this grasping of himself. As even these slight reflections show, the task of fulfilling the Oracle's injunction involves a certain mystery. Either the self is empty or it involves everything. The circle of my apprehending myself apprehending myself is, in its self-reference, devoid of content. Content seems to arise once I admit that, knowing myself, I do not know an object. I know that by which objects are known. Here I assert that the self is that in and through which they are present. Its mode of presence is their modes of coming to presence. As such, it hides itself behind them. Presenting itself as their place, it itself seems placeless. Its content is given by its objects and their modes of appearing. This implies that to know it, I would have to know what could fill it, what objects I could possibly know. For this, however, I would have to know the knowable world itself. Is the self then a world? It does not seem so. Embodied, it is subject to various accidents, including injury, decay, and death. Psychologically, it also has its vulnerabilities, its habits, its peculiarities. An entity among entities, a being within the world, how can it claim to be a world?