In the historiography of the 18th century German philosophy and literature, the German tradition of language-based epistemology is largely overshadowed by the attention given to rationalist thought currents. The tradition of thought harking back to Leibniz' concept of cognitio symbolica and to English empiricism as represented by Bacon and Locke is frequently neglected, although this approach with its reconciliation of rationalist and empiricist elements was sustained until the end of the 18th century. With reference to empirically verifiable sources, the present study undertakes a systematic outline of the evolution of a semiotic concept of knowledge as reflected in the theoretical writings of the important philosopher and scientist Johann Heinrich Lambert (1728-1777), in the consistent incorporation of that concept in Herder's "Metakritik" and in the poetological account it is turned to in Jean Paul's "Vorschule der Ästhetik" and Novalis' 'theoretical' works.