This chapter examines Cassirer's view on contemporary science. It revisits Cassirer's lesser-known work Determinism and Indeterminism in Modern Physics and argues that it harbors a significantly new stage of his philosophy of physical science. On the one hand, this work presents the quantum formalism as a limiting pole of the Bedeutungsfunktion, the highest mode of symbolic formation according to Cassirer’s “phenomenology of cognition.” Inspired by Paul Dirac, Cassirer understands quantum mechanics as a symbolic calculus for deriving probabilistic predictions of measurement outcomes without regard to underlying wave or particle “images” – or, as an exemplar of abstract symbolic thought. On the other hand, Cassirer recognizes the philosophical significance of the use of group theory in quantum mechanics as advancing a purely structural concept of object in physics. Hence, Ryckman reveals that Cassirer drew epistemological consequences from the symbolic character of contemporary physical theory that retain relevance for philosophy of science today.