After unpacking the sense in which Heidegger uses the term "contradiction," the chapter reviews his use of it in the strictly logical, “injunctive” sense as the “principle of non-contradiction” (PNC) and “law of thinking,” particularly as he wields it in the course of exposing what otherwise appear to be cases of vagueness or ambiguity. It then reviews his tendency in some contexts to align the PNC with a metaphysics that restricts being to being on hand (vorhanden) and the dilemma that this ontological interpretation presents, given his apparent adherence to the principle, even as he proposes a broader understanding of being. The chapter then suggests that his analysis of attunement in the 1929/30 lectures introduces a more expansive reading of the PNC and that this reading is corroborated by his existential interpretation of the principle in the Winter Semester of 1933/34. The interpretation is a ringing endorsement of the PNC and the sameness of reference it enjoins as a condition for being-with-one-another. The chapter concludes by probing the implications of this ontologically broader – or post-ontological – interpretation of the PNC for thinking and speaking of being itself, riddled with “nothingness” as it is.

Difference is a condition of being separate and dissimilar, on the basis of which we are capable of drawing distinctions. We typically distinguish between entities within the same or approximately the same domain (e.g., black and white, house and garden), between entities in different domains (e.g., God and the number five), and between different domains of entities (e.g., chemical and psychological agents). Not to be confused with any of these differences, though underlying all of them, is the most essential difference: the difference between entities and being.

Situating Cassirer in a historical perspective, Daniel D. Dahlstrom's chapter casts light on prominent lines of convergence and divergence between Husserl’s phenomenological analyses and Cassirer’s philosophical studies. The general topic of the first line of convergence is logical theory, as Husserl and Cassirer both argue for the autonomy of logic, the promise of set theory, and the intensionality of concepts.Other lines of agreement include their common rejection of empiricist accounts of abstraction and universals, their embrace of a Kantian philosophical legacy, and their respective commitments to the primacy of meaning and self-described versions of idealism. Nevertheless, the philosophies of Husserl and Cassirer diverge from one another in significant ways, primarily in view of the thematic range of their investigations and their respective insistence upon intuition and the sign or symbol as the basis of human consciousness and cognition. Dahlstrom focuses on differences in Husserl and Cassirer's analyses of intuitions and perceptions that Cassirer himself also pronounced.