[Side-note: Reasonings of Diodôrus--respecting Hypothetical Propositions--respecting Motion. His difficulties about the _Now_ of time.] But if he reproduced the arguments of Zeno, he also employed another, peculiar to himself. He admitted the reality of _past_ motion: but he denied the reality of _present_ motion. You may affirm truly (he said) that a thing _has been moved_: but you cannot truly affirm that any thing _is being moved_. Since it was _here_ before, and is _there_ now, you may be sure that it has been moved: but actual present motion you cannot perceive or prove. Affirmation in the perfect tense may be true, when affirmation in the present tense neither is nor ever was true: thus it is true to say--Helen _had_ three husbands (Menelaus, Paris, Deiphobus): but it was never true to say--Helen _has_ three husbands, since they became her husbands in succession.[69] Diodorus supported this paradox by some ingenious arguments, and the opinion which he denied seems to have presented itself to him as involving the position of indivisible minima--atoms of body, points of space, instants of time. He admitted such minima of atoms, but not of space or time: and without such admission he could not make intelligible to himself the fact of present or actual motion. He could find no present _Now_ or Minimum of Time; without which neither could any present motion be found. Plato in the Parmenidês[70] professes to have found this inexplicable moment of transition, but he describes it in terms not likely to satisfy a dialectical mind: and Aristotle denying that the Now is any portion or constituent part of time, considers it only as a boundary of the past and future.[71] [Footnote 69: Sextus Empir. adv. Mathemat. x. pp. 85-101.] [Footnote 70: Plato, Parmenidês, p. 156 D-E. [Greek: Po/t' ou)=n, metaba/llei? ou)/te ga\r e(sto\s a)\n ou)/te kenou/menon meta/balloi, ou)/te e)n chro/nô| o)/n]. (Here Plato adverts to the difficulties attending the supposition of actual [Greek: metabolê/], as Diodorus to those of actual [Greek: ki/nêsis]. Next we have Plato's hypothesis for getting over the difficulties.) [Greek: A)=r' ou)=n e)sti/ to\ a)/topon tou=to, e)n ô)=| to/t' a)\n ei)/ê o(/te metaba/llei? To\ poi=on dê/? _To\ e)xai/phnês; ê( e)xai/phnês au)/tê phu/sis a)/topos_ tis e)gka/thêtai metaxu\ tê=s kinê/seôs te kai\ sta/seôs, e)n chro/nô| ou)deni\ ou)=sa, kai\ ei)s tau/tên dê\ kai\ e)k tau/tês to/ te kinou/menon metaba/llei e)pi\ to\ e)sta/nai kai\ to\ e)sto\s e)pi\ to\ kinei=sthai]. Diodorus could not make out this [Greek: phu/sis a)/topos] which Plato calls [Greek: to\ e)xai/phnês].] [Footnote 71: To illustrate this apparent paradox of Diodorus, affirming past motion, but denying present motion, we may compare what is said by Aristotle about the Now or Point of Present Time--that it is not a part, but a boundary between Past and Future.