The dissertation argues that a necessary limitation to the attainment of full autonomy arises from the structure of reasoning itself as a discursive practice. In contrast to Kant's conception of human psychology as a contingent source of forces that tend to undermine our potential for full autonomy as rational beings, the dissertation identifies an epistemic constraint that necessarily limits the scope of autonomy for all rational beings, granted that reasoning is understood as rule-following. To that end, the dissertation defends an interpretation of the so-called regress of rules argument with a view to the foundations of rational agency. According to that interpretation, practical reason is based on an implicit bedrock of norms that are enacted in a social practice without being known as such by the participating subjects. Though one can always make such implicit norms explicit by representing the patterns of concept-use in a given discursive practice, thus bringing unreflected habits of thought to the attention of rational assessment, it is a necessary structural feature of reasoning that its fundamental normative structure lies hidden, because unrepresented, in socially entrenched dispositions. This epistemic finitude reveals, against the key tenet of the Kantian tradition, that we can be the source of the norms we follow as rational beings only against a background of norms that escape our discursive attention and thus endorsement — i.e., that autonomy, in fact, presupposes heteronomy. The dissertation aims to demonstrate in exegetical detail that the resultant view of power and freedom as two mutually dependent components in the structure of reasoning constitutes the conceptual core at the center of Michel Foucault’s philosophical work that enables one to articulate a hitherto neglected systematic unity between his apparently disparate investigations into archaeology of knowledge, genealogy of power, and ethics as self's relation to itself. When reconstructed from this perspective, Foucault’s work is used, in turn, to illustrate how the notion of autonomy and especially the topic of self-constitution need to be reconceptualized, in contrast to some of the current approaches in Kantian ethics.