The present study establishes the concept of transcendental semblance (Schein) as the architectonic key to the understanding of Husserl’s mature phenomenology as a post-Kantian transcendental philosophy. It argues that the idea of transcendental semblance functions as the operative foundation for Husserl’s demarcation between the transcendental and mundane realms of experience. This demarcation is shown to be necessitated by the phenomenological reduction as Husserl’s critique of knowledge, in the same systematic manner that the idea of transcendental illusion (Schein) grounds Kant’s distinction between phenomena and noumena necessitated by his critique of pure theoretical reason. Through a genealogical reconstruction of the immanence–transcendence problem in Kant, Brentano, and the early Husserl (of the Logical Investigations), this study exposes the structural tensions that would render a merely descriptive and eidetic psychology insufficient. It demonstrates that Husserl’s ‘transcendental turn’ was not an estrangement, but the methodological and teleological fulfilment of the epistemological project initiated in the Logical Investigations, in light of his predecessors. By thoroughly examining Husserl’s determination of the natural world as a transcendental semblance in Ideas I, supplemented by his Nachlass manuscripts, the thesis vindicates Husserl’s transcendental idealism as the only rigorous solution to the accessibility problem of cognition. Ultimately, by securing the foundational sphere of ‘condition of possibility’ for human experience against naturalism, this investigation lays the methodological groundwork for a phenomenology of radical transcendencies — Body, Other, and Divine — that are not fully dissolvable to the immanent genesis of objectivations.