The paper investigates a strand of Patočka's phenomenological appropriation of Plato in Plato and Europe — what is there termed the "ontocosmic" dimension proper to care of the soul — and argues that this appropriation is fundamentally influenced by the "so-called unwritten doctrine." This doctrine, and not the influence or anticipation of Heidegger's notion of Sorge, is shown as the basis for Patočka's claim that "what shows the activity of the soul in the proper sense is our relation to the mathematical world." The investigation of Patočka's account of care for the soul also explores the influence of Jacob Klein's reconstruction of the "Ideas-numbers" in the Platonic doctrine on Patočka's presentation of the chōrismos thesis, which is inseparable from this doctrine. It is argued that this thesis is a major factor in Patočka's notion of the fundamental distinction between (1) what manifests itself and (2) manifesting, and that this distinction informs his critique of Husserl's and Heidegger's phenomenological subjectivism, together with his own concept of the phenomenon proper to phenomenology. The paper concludes by pointing out certain problems in Patočka's critique of the metaphysical character of the Platonic account of "the appearing of being" that follow from his endorsement of Konrad Gaiser's reconstruction of the "dimensional generation" of solids as a fundamental aspect of Platonism. These problems are located in Gaiser's reversal of the Republic's (Book VI) account of the image-paradigm distinction as it relates to mathematical hypotheses and eidē, and the paper ends by suggesting that the restoration of the proper order to this relationship holds the key to substantiating Patočka's original thought: that the structure of manifesting has to be "something more" than what appears, if it is to appear.