The ἀπορίαι in Physics 217b33–218a30

Aristotle asks whether time belongs to the category of things that exist or not, and argues that if it does its existence is so uncertain that it merits the question ‘What then is it?’ The enquiry into the aporiai requires a careful study and translation of the Greek text as a basis for a precise exegetical analysis. Aporia 1: Time is composed of past and future time. Time is always subjectively and cognitively perceived, a key point in Aristotle’s thought on time that often is neglected. By the use of the optative δόξειε ‘might seem’ in regard to the issue as to whether time may partake in substance or not, Aristotle tentatively keeps the door open for such a possibility. Aporia 2: time, as opposed to objects in general, consists of non-existing parts. The ‘now’ (that does exist) is not a part. Aporia 3: The ‘now’ is presented as either the same ‘now’ or as a series of different ‘nows.’ Two ‘nows’ cannot co-exist nor can they follow one another back to back. The one and same ‘now’ in the extended sense cannot continue indefinitely; if so there would be no ‘before’ and no ‘after,’ and all things throughout history would co-exist. The ‘now’ is a divider of time. The limithood of the ‘now,’ constantly marking out the limit between past and future, is cognitively perceived.