In this chapter, I examine arguments that have been or might be used to establish or defend the distinction that Heidegger draws between entities (things that are) and the being of entities (that by virtue of which those things are). I find these arguments for the ontological difference to fail – due largely to the self-concealing nature of being, which makes it difficult to distinguish being from entities. At the same time, I see something positive in these troubles for the ontological difference, that is, they serve as prompts to question the meaning of being.

This chapter reconstructs Heidegger’s 1955–56 interpretation of the principle of reason as a principle that resonates or sounds variously in the history of philosophy. The principle is first fully formulated by Leibniz as the principle of sufficient reason, which states that there is no true fact or proposition without sufficient reason for it being so and not otherwise. Heidegger takes Leibniz’s principle of sufficient reason to be a historically specific version of the principle of reason, which is a fundamental ontological principle holding that nothing is without a reason or ground, and so that being is ground/reason. Heidegger hears this association between being and ground resonating in the ancient Greek concept of logos, which is taken up but distorted by the Romans in the concept of ratio. From there, the ontological principle develops into the principle articulated by Leibniz and comes to express the distinctive commitments of modern philosophy and technology. While Heidegger’s historical story is not entirely plausible and contains significant omissions, attempting to reconstruct it reveals why this purported history of the principle of reason is relevant to Heidegger’s broader ontological project.

“Thrownness” is first used in Being and Time to name Dasein’s passive coming into being open, and so Dasein’s birth, origin, or ground. Heidegger continues to describe Dasein as thrown in his later thought, closely associating thrownness with adaptation (Ereignis) and identifying the “thrower” of the throw into existence as being. Especially in Being and Time, the pure throw into Dasein continues as a throw into concretion (facticity), falling, and inauthenticity, although it is not entirely clear how these phenomena are both connected to and distinguished from one another.

Uncanniness is how one is in the fundamental disposedness of anxiety (SZ) and later “the basic trait of the human essence” (GA40:160/168). In Being and Time, it appears to be an unsettled feeling produced by a breakdown in familiarity, while in later lecture courses “uncanniness” usually names a presencing that occurs by way of an absencing.

Anxiety is a fundamental disposedness or fundamental mood in which Dasein is exposed to a threat in its own being. In contrast, fear is a mood in which a case of Dasein is open to threats in its environment. Heidegger analyzes fear (Furcht) in Being and Time in order to illustrate the phenomenon of disposedness and he analyzes anxiety (Angst, also translated as “angst” or “dread”) in order to explain falling and reveal the unity of care.

Mood is the fundamental way in which Dasein is open to itself and its world. It is a mode of disposedness (Befindlichkeit) and so of self-finding, in which Dasein is attuned to itself and its surroundings in some determinate way. Mood is equiprimordial with understanding (Verstehen), and with it is constitutive for Dasein’s disclosedness.