Does adherence to the principles of logic commit us to a particular way of viewing the world? Or are there ways of being – ways of behaving in the world, including ways of thinking, feeling, and speaking – that ground the normative constraints that logic imposes? Does the fact that assertions, the traditional elements of logic, are typically made about beings present a problem for metaphysical (or post-metaphysical) prospects of making assertions meaningfully about being? Does thinking about being (as opposed to beings) accordingly require revising or restricting logic’s reach – and, if so, how is this possible? Or is there something precious about the very idea of thinking the limits of thinking? Contemporary scholars have become increasingly sensitive to how Heidegger, much like Wittgenstein, instructively poses such questions. Heidegger on Logic is a collection of new essays by leading scholars who critically ponder the efficacy of his responses to them.

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.

The worldis the unfolding complex of actual and possible relationships that matter to human beings. In this complex of relationships, human beings essentially find and define themselves, others, and the things around them, while also being defined by the latter. The world is not to be confused with any entity or thing within it. Since taking something to be is typically construed as convertible with taking it to be an entity, Heidegger cautions against claiming that the world is. In order to ward off the possibility of construing the existence (the ontological status) of this complex with that of anything else (especially things, tools, objects within it as well as the subject-matters of any particular science), Heidegger early on coins the neologism “worlding” (welten), to which he frequently has recourse later (GA56/57:73; GA9:164/126; GA7:181/PLT 177; GA12:26/PLT 203; GA5:30f/22f; GA38:168/140).

An open is a domain in which things are easily accessible or exposed. As long as things lie hidden from us, we have no access to any truths concerning them. They have to come out or be brought out into the open, and it is equally necessary that we occupy a suitable place in the open and be open to them. Heidegger adapts these ordinary nominative, adjectival, and verbal uses of “open” and “openness” to characterize truth as unconcealment.

Differenceis 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.