Although Kantian Copernican Revolution makes the subject the determinant center of philosophical examination, the transcendental subject, which is the necessary condition for the systematic unity of reason, remained incapable to constitute this unity because of the ambiguity in its definition, i.e. Kantian system with all the dualities that are brought with the gap between theoretical and practical reason like universal and individual, concept and intuition, thought and being, subject and object, ego and nonego and human and nature could not be completed. Since making a claim of being a philosophical system cannot be separated from the success of overcoming the supposed dualities, post-Kantian German Idealists undertook the task to sublate all these dualities, Fichte and Schelling, in particular, argue that this task can be fulfilled by finding the first principle from which all laws can be derived. In this paper, we examine why and on which point these two philosophers dissent with each other. Since this controversy depends on the question of what should be understood by self and not-self and how can their relation be established, this conflict between them also reveals the difference between their conceptions of nature. Hence, while for Fichte, who defends the constituent priority of practical reason and spontaneity of subject, nature is just an instrument for human being, for Schelling, who focuses on the idea of purposive nature, which cannot be demonstrated discursively in Kantian system, human being is a part of holistic nature. Herewith, we can say that the difference between the conceptions of nature of two philosophical systems one of which favours thought over being, and concept over intuition as its starting point and the other of which asserts that being precedes thought, and intuition precedes concept exhibits a sort of intellectual map through which one can conceive of today’s ecological concerns.