Before dwelling on this paradoxical self-undermining of the principle of reason, I begin by stressing that Heidegger considers our present age to be entirely ruled and “held in the sway of the fundamental principle of rendering sufficient reasons” (GA 10, 187/PR, 128). This principle states that “‘for every truth’ (which means, according to Leibniz, every true proposition) ‘the reason can be rendered’” (GA 10, 34/PR, 22). This principle in fact defines what science answers to (although science does not reflect upon it but is rather driven by it), as Heidegger makes the claim that “the demand to render reasons is, for the sciences, the element within which its cognition moves, as does the fish in water and the bird in air” (GA 10, 46–47/PR, 30). In fact, science as such rests upon and answers to the demand of the principle of reason: “Science responds to the demand of ratio reddenda and does so unconditionally. Otherwise, it couldn’t be what it is” (GA 10, 47/PR, 30). Indeed, the principle of reason permeates and rules our entire human existence and historical age to such an extent that in fact it not only rules science but philosophy as such. “The principium rationis as thought by Leibniz not only determines, by the sort of demand it makes, modern cognition in general, but it permeates in a decisive manner that thinking known as the thinking of thinkers—philosophy. As far as I can see, the full import of this fact has not yet been thought through” (GA 10, 64/PR, 43). Further, Heidegger stresses that the scope of the principle of reason is not limited to “the demand of reason to be rendered . . . as an abstract rule of thinking,” for it involves the “practical” scope of an ordering and transformation of nature itself as well as humanity. “The demand was bepowering in a strange way, namely, that the energies of nature as well as the mode of their procurement and use determine the historical existence of humanity on earth” (GA 10, 83/PR, 56).
It is matter of rendering reasons to a demand for a reason. Heidegger insists on the “demand-character of reason,” of ratio as ratio reddenda. “What is bepowering about the principle of reason is the demand that reasons be rendered” (GA 10, 42/PR, 27). And therefore, the reddendum, “the demand that reasons be rendered, now speaks unabatedly and without surcease across the modern age and out over us contemporaries today. The reddendum, the claim that reasons be rendered, has insinuated itself between the thinking person and their world in order to take possession of human cognition in a new manner” (GA 10, 37/PR, 24). Ultimately, Heidegger considers the “reign” of the “mighty” principle of reason—the demand to render (sufficient) reasons—to be the great uprooting of authentic humanity. Commenting upon the “strange” normative power that the principle of reason has on our lives, he writes: “When I use the word ‘strange’ [unheimlich] here, I mean it not in a sentimental sense. One must think it in both a literal and substantive sense, namely, that the unique unleashing of the demand to render reasons threatens everything of humans’ being-at-home and robs them of the roots of their subsistence, the roots from out of which every great human age, every world-opening spirit, every molding of the human form has thus far grown” (GA 10, 47/PR, 30). His critique is quite severe, as he continues by claiming that “the claim of the mighty Principle of rendering reasons withdraws the subsistence from contemporary humanity” (GA 10, 47/PR, 30) and that “the more decisively humans try to harness the ‘mega-energies’ that would, once and for all, satisfy all human energy needs, the more impoverished becomes the human faculty for building and dwelling in the realm of what is essential” (GA 10, 47/PR, 30–31). In short, as he concludes, the demand to render reasons amounts to a “withdrawal of roots” (GA 10, 47–48/PR, 31). In fact, the dominance of the principle of reason corresponds to “the most extreme withdrawal of being” (GA 10, 83/PR, 56). This withdrawal corresponds to the project of total calculability of the real, which goes hand in hand with the project of reducing the event, that is, what is eventful in the event.
This discussion will proceed step by step. Heidegger begins by recalling what the principle of reason states, namely that nihil est sine ratione: nothing is without a reason. It asks for a reason so that nothing is without a why: “Nihil est sine ratione. Nothing is without reason. There is nothing—and here that means everything that in some manner is—that is without reason” (GA 10, 6/PR, 5). The principle of reason is a statement about beings as a whole, affirming that every being has a reason, as well as a cause, since Heidegger reminds states that Leibniz had included in the principle of reason a principle of causality. Now, the expression “nothing is without a reason” (or a cause) can be heard positively or negatively. “Nothing is without a sufficient reason, which demands to be rendered. In the affirmative form this means that every being has its sufficient reason, which must be rendered. In short: ‘nothing is without reason’” (GA 10, 75/PR, 50). This last expression contains a double negation, which Heidegger understands as concealing an affirmation regarding the meaning of being: “What immediately strikes us about this formulation of the principle of reason is that it contains two negations: Nihil-sine; nothing-without. The double negation yields an affirmation: nothing that in any manner is, is without a reason. This means that everything that is, every being whatsoever, has a reason” (GA 10, 6/PR, 5, emphasis mine). There must be a reason why there is something rather than nothing. “There is a reason in the nature of things why something exists rather than nothing” (GA 10, 42/PR, 27). The principle of reason demands that everything that happens be founded in reason. This principle is first of all a request, a demand, a claim and a command (Anspruch), a call to render reasons, the call of the ratio reddenda: that everything, every being, shows or reveals its reason or foundation. The principle of reason is a demand for foundation, for an ultimate Grund. The rendering of reason is a response to a demand, the demand to establish a sufficient foundation for all that is. “Sufficient” here means, as Heidegger states in the Address, the “completeness of a foundation” (GA 10, 177/PR, 121). The rendering of reason amounts to a rendering of grounds. “Accordingly, the strict formulation of the principium rationis as the principium reddendae rationis contains a very specific and decisive explanation of what the unrestricted principle of reason says: nothing is without reason. This now says: something ‘is,’ which means, can be identified as being a being, only if it is stated in a sentence that satisfies the fundamental principle of reason as the fundamental principle of founding” (GA 10, 36/PR, 23, emphasis mine). The call for foundation is the true calling of the principle of reason. This is indeed why the principle of reason has an ontotheological structure as it refers to an unconditioned and ultimate foundation for all beings or nature, namely God. Heidegger clarifies that for Leibniz the principle of reason participates to the ontotheological structure of metaphysics, which posits a supreme being at the foundation of all beings and accounts for beings by appealing to yet another being: “However, because Leibniz and all metaphysics come to a halt with the principle of reason as a fundamental principle about beings, metaphysical thinking requires, according to the fundamental principle, a first reason for being: in a being, and indeed the being that is most of all” (GA 10, 184/PR, 125). As Heidegger explains, for Leibniz there is in the nature of things “a reason why something is rather than nothing. As the first existing cause of all beings, God is called reason” (GA 10, 42/PR, 27). Thus, “what is to be posited as the ultima ratio of Natura, as the furthest, highest—and that means the first—existing reason for the nature of things, is what one usually calls God” (GA 10, 42/PR, 27). At the same time, this ontotheological structure of the principle opens onto a circle: “So the principle of reason holds only insofar as God exists. But God exists only insofar as the principle of reason holds. Such thinking moves in a circle” (GA 10, 43/R, 28).
Heidegger makes a further—and decisive—claim: the principle of reason can be taken as a statement on beings, or else as it pertains to being as such. He writes: “We can hear the principle of reason in a twofold manner: on the one hand, as a supreme fundamental principle about beings, and, on the other hand, as a principle of being” (GA 10, 100/PR, 68). First, Heidegger begins by insisting on the ontological (rather than epistemological or metalinguistic) scope of