Translated by Pete Ferreira
Regardless of the many questions that Aristotle tackles in the second chapter (Phys. IV, 11) of his discussion of time, Heidegger focuses especially on the fundamental assertion of all Aristotelian theories of time, namely the famous definition, according to which time is the number of the movement according to before and after (τοῦτο γαρ ἐστίν ὁ χρόνος, αριθμός κινήσεως κατά τὸ πρότερον καὶ ὕστερον, 219b 1-2). Among the problems that this definition raises, and which Heidegger points out, is first that of showing how the experience of movement implies that of time, and also that of determining the concept of number and instant.
In the next chapter (Phys. IV, 12) a concept is introduced and determined that is fundamental in Heidegger's eyes, namely the concept of being-in-time (τὸ ἐν χρόνῳ εἶναι), translated with the German term Innerzeitigkeit. The explanation given by Aristotle, saying that it is in time what their existence is measured with time, it is critical to understanding the connection between movement and time, given that not only the movement, which is in time, is measured by time, but also the very same time is measured according to movement. In connection with the determination of the concept of 'intratemporality' other fundamental questions are posed, with which Heidegger mainly emphasizes the relationship between number and time, between time and stillness, and finally the relationship between time in its three dimensions and what is outside of it, that is the extra-temporal.
According to Heidegger the central problem of the penultimate chapter (Phys. IV, 13) is that of the unity of time in the multiplicity of the succession of moments, of 'nows', the problem of showing how the instant, the now (το νυν), as the basic unit which all temporal determinations must be attributed, constitutes the basis of the continuity (συνέχεια) of time. It is in this context that determinations of ἤδη, ἄρτι, πάλαι and ἐξαίφνης are laid out.