Abstract: Ideals of authentic, autonomous selfhood are central to the Enlightenment. This dissertation argues that these ideals give rise to paradoxical structures of theatricality, in which the body becomes most meaningful as a sign for the inner truth of the soul when it silences the subject's voice. The body stages a performative immediacy but thereby also acquires a significance that this dissertation elucidates as poetic. The term 'poetic' refers to literary practices from the eighteenth and nineteenth centuries in Germany and France that reflect upon the limits of embodied subjectivity, on speech as a medium for subjective action and expression, and on forms of community such as the public sphere or the body politic without which the self would be a solipsistic monad. The dissertation therefore aims to understand why this theatricality produces a tension between the voice and the body and what it means that this tension resolves in poetic language. Analyzing the philosophical tradition of mind from Descartes to Leibniz, Rousseau, and Kant, the dissertation first shows how the inner activity of thinking gives rise to a paradoxical theatricality that invests the body with poetic significance and thereby interrogates the conditions of possibility of communicating sentiments. With Kant, the ideal of a sensus communis culminates in the claim that complete communication can occur only in meaning that is poetic because it is devoid of determinate content. Reading works by Lessing, Klopstock, Hamann, and J.J. Engel, the dissertation then examines literary, hermeneutic, and theatrical practices that explore the power of the body to function as a natural sign of the soul and broach the possibility that language itself might manifest powers of gesture and movement. In these practices, poetic language founds concrete forms of community, but the limits of these communities uncover a tragic structure in which a subject is caught between the apparent immediacy of its body and the need to express itself in language. Finally, in a reading of Georg Büchner's historical drama Dantons Tod, the dissertation argues that this play's intertextuality confronts this tragic structure with a poetic freedom that arises only in challenging its own possibility.