Hermann Lotze was an important influence for founding philosophers in major contemporary philosophical methodologies such as pragmatism (e. g. William James and Josiah Royce), phenomenology (e. g. Edmund Husserl), and analytic philosophy (e. g. Gottlob Frege). This chapter focuses on Lotze’s Logic for clues to Lotze’s widespread appeal to various contemporary philosophical movements. In particular this essay explores the logical status of Lotze’s Sigma as the sought but not yet fully understood subject. By finding in Sigma a shared term between idealistic and empirical sciences, Lotze provides an interpretive middle ground between pure (a priori) and applied (a posteriori) logic, as well as between purely logical scientific inquiries (as are found in mathematics and philosophy, for instance), and applied logical inquiries into the nature of the world (as for instance in the natural sciences). Sigma may have been a powerful influence on the phenomenologists, pragmatists, and analytic philosophers who followed, having shown a way beyond seeming dichotomies of idealism vs. empiricism. Lotze shows the fruitful interaction between these two modes of logical science but also their uniqueness; in turn, he shows how logic is both a unique philosophical science and also valuably related to ethics and metaphysics.