  Unlike the “Kallias” letters, Schiller’s essay “On Naïve and Sentimental Poetry” was immediately influential. Here Schiller describes the difference between “naïve” and “sentimental” art. The former is an expression of an immediate emotional response to nature, where nature is thought of as “the subsistence of things on their own, being there according to their own immutable laws” (a conception of nature that derives from the conception of beauty in the “Kallias” letters). The latter self-consciously expresses a sense of our own separation from nature and a feeling that the self-subsistent things in nature “are what we were” and “what we should become once more” (“Naïve and Sentimental Poetry,” pp.  180–1), or a longing for a wholeness with nature that we think humans once had but that we have lost. Schiller identifies naïve poetry with antiquity and sentimental poetry (and the sense of alienation from nature it expresses) with modernity.  This essay can be seen as the source for the genre of philosophical histories of aesthetics that then flourished for several decades, beginning with Friedrich Schlegel’s “On the Study of Greek Poetry” of 1797, continuing with Friedrich Wilhelm Joseph Schelling’s lectures on The Philosophy of Art of 1802–3, and culminating in the lectures on “Philosophy of Art or Aesthetics” that Hegel gave in Berlin during the 1820s—lectures that decisively changed the sense of the name “aesthetics” itself from its original meaning of a general science of sensibility that included responses to nature as well as art to its modern meaning as the philosophy of art.