This is the way time as the persistent is presented in the principle of the First Analogy: “In all change of appearances substance persists” (B 224).

If a time-determination is to be possible at all, this principle is the a priori condition that rules and renders determinable all time-relations. It is born of the necessity of rendering a determination of time a priori possible as regards the unity of the transcendental apperception, since time itself is a priori not perceivable. This principle stands “at the head of the pure and completely a priori laws of [353] nature” (B 227). It is the principle that expresses the conditions of the possibility of the objectively determinable being-in-time of nature. It establishes a priori how any entity-that-is-in-time must be at each moment if it is to be determinable, in accordance with its objective being-in-time, as this entity that is in time at every moment. As the principle of “existence in time,” it expresses a general time-determination, i.e., a rule of time-relations as such. In this case it expresses the fact that something which persists must underlie all one-after-another and at-the-same-time. Only by way of this permanent something is existence endowed, in the various parts of time, with a magnitude, in the sense of quantitas, a magnitude that we call “duration.” As Kant says, duration is the “magnitude of existence” (B 262), the magnitude of presence {Anwesenheit}—i.e., the measure of “how long,” from when to when. And every “when” is determinable by a “then,” and this “then” is a “now.” The determination of the now, of the how-long, and of duration are possibly only on the basis of this something-persistent.

If an objective knowledge of nature is to be possible, the unity of the transcendental apperception requires that there be something that persists. You see that, given this observation, new determinations of time emerge. Likewise it already becomes clear how time functions in a specific way (to put it roughly) in the transcendental apperception’s movement toward or transcending to the world. For Kant’s original Cartesian position itself requires that the a priori necessary conditions of this movement must be exhibited; and this movement itself, in its necessity, is nothing else that the whole of the presuppositions that underlie every empirical time-determination and time-reckoning. In every indication of time there reside the principles formulated in the analogies, and primarily the principle of the First Analogy, “In all change of appearances substance persists”—a principle that is not gotten from, but rather underlies, all empirical experience.¹¹¹

111. [Here (Moser, p. 705) Heidegger ends his lecture of Monday, 15 February 1926, to be followed by that of Tuesday, 16 February, which opened with a 700word summary that is omitted in GA 21.]