For a long time, Friedrich Schlegel’s thought was considered and interpreted exclusively as critical of systems. However, this view does not correspond to Schlegel’s own understanding of his thought. In fact, Schlegel takes a position that draws attention to the problems of overly rigid systematic concepts without abandoning the systematic claim of philosophising. After a brief overview of his early system thinking, the article focuses on Schlegel’s critique of strict philosophical systems, on the one hand, and his own claim to a system, on the other. It is shown how Schlegel, in distinction from Fichte and Spinoza, develops the idea of a connection between systematic claims and system critique or, put another way, between system and systemlessness. Only such an open system model is suitable for adequately reflecting the dynamic nature of philosophising. Schlegel put this claim forward for the first time in his Jena Lecture on Transcendental Philosophy of 1800/1801. The Lecture must be understood as a system in the process of becoming, open to development, incomplete and consequently relative, which comprises a multitude of historically evolving systems and which can only adequately be represented through the interplay of philosophy and poetry.