§24. _Natura_: this word, it is important to observe, has to serve as a translation both of φυσις and ουσια. Here it is ουσια in the broadest sense, all that exists. _In res duas_: the distinction between Force and Matter, the active and passive agencies in the universe, is of course Aristotelian and Platonic. Antiochus however probably apprehended the distinction as modified by the Stoics, for this read carefully Zeller, 135 sq., with the footnotes. The clearest view of Aristotle's doctrine is to be got from Schwegler, _Handbook_, pp 99--105. R. and P. 273 sq. should be consulted for the important coincidence of Force with logical _genus_ (ειδος), and of Matter (‛υλη) with logical _differentia_ (διαφορα). For the _duae res_, cf. _D.F._ I. 18. _Efficiens ... huic se praebens_: an attempt to translate το ποιουν and το πασχον of the _Theaetetus_, το οθεν and το δεχομενον of the _Timaeus_ (50 D). Cic. in _Tim._ has _efficere_ and _pati_, Lucretius I. 440 _facere_ and _fungi_. _Ea quae_: so Gruter, Halm for MSS. _eaque._ The meaning is this; passive matter when worked upon by an active generative form results in an _aliquid_, a τοδε τι as Aristotle calls it. Passive matter ‛υλη is only potentially τοδε τι, passing into actual τοδε τι, when affected by the form. (Cf. τοδε, τουτο, Plato _Tim._ 49 E, 50 A, also Arist. _Metaph_ H, 1, R. and P. 270--274). A figurative description of the process is given in _Timaeus_, 50 D. _In eo quod efficeret ... materiam quandam_: Cic. is hampered by the _patrii sermonis egestas_, which compels him to render simple Greek terms by laboured periphrases. _Id quod efficit_ is not distinct from, but _equivalent_ to _vis_, _id quod efficitur_ to _materia_. _Materiam quandam_: it is extraordinary how edd. (esp Goer.) could have so stumbled over _quandam_ and _quasi_ used in this fashion. Both words (which are joined below) simply mark the unfamiliarity of the Latin word in its philosophical use, in the Greek ‛υλη the strangeness had had time to wear off. _In utroque_: for _in eo quod ex utroque_ (sc. _vi et materia_) _fit_, the meaning is clearly given by the next clause, viz. that Force and Matter cannot actually exist apart, but only in the compound of the two, the formed entity, which doctrine is quite Aristotelian. See the reff. given above. _Nihil enim est quod non alicubi esse cogatur_: the meaning of this is clear, that nothing can _exist_ except in space _(alicubi)_, it is more difficult to see why it should be introduced here. Unless _est_ be taken of merely phenomenal existence (the only existence the Stoics and Antiochus would allow), the sentence does not represent the belief of Aristotle and Plato. The ιδεαι for instance, though to Plato in the highest sense existent, do not exist in space. (Aristotle explicitly says this, _Phys._ III. 4). Aristotle also recognised much as existent which did not exist in space, as in _Phys._ IV. 5 (qu. R. and P. 289). Cic. perhaps translates