Fechner's very specific theory of cosmological evolution constitutes the core of his philosophy. In a very detailed analysis, Heidelberger develops its methodological foundations, constantly emphasizing Fechner's deep and far-reaching empiricism and the lasting importance of concepts shaped by him. This holds, in particular, for his notion of causality which — through Ernst Mach — became pioneering for modern epistemology. For Fechner, the law of causality consisted in relatively free, but nonetheless categorically valid, functional dependencies and relations between causes and effects. Heidelberger demonstrates that this important step originated in Fechner's metaphysically motivated opposition against contemporary materialism and the latter's strictly deterministic understanding of the law of causality. The author's detailed reconstruction shows how the conceptual basis of Fechner's all-pervasive indeterminism developed and resulted in a — highly modern — conception of cosmological evolution that comprised the inanimate nature as well.