As an interpretive introduction to the “second phase” of the moral theory of F. Miró Quesada (1918), the article analyzes his three last ethical works in order to examine how he attempts to refine Kantian deontology, overcome its apparent limitations -disguised materialism, empty formalism, and absurd dualism-, and rethink the moral law as a coin with symmetry and non-arbitrariness on each side. Special attention is paid to symmetry as a sufficient condition for ethics.