228 THE SCIENCE OF LOGIC 



conclusion, expresses the real cause of the fact stated in the conclusion. This 

 is essentially the Aristotelian doctrine.&quot; l 



Fourthly, the premisses must be really prior to the conclusion, 

 inasmuch as the middle term of a demonstration is the &quot;cause,&quot; 

 and this is naturally prior to its effect. When there is question 

 of a physical efficient cause, which produces its effect by means 

 of motion or physical change, the cause must precede the effect 

 in time, because motion, being successive, involves duration? 

 But it is not essential to a real or ontological principle that it 

 be prior in time to what proceeds from it. For instance, the 

 formal and material causes, which are the real, intrinsic, consti 

 tutive principles of any material being, need not necessarily exist 

 prior to the being that is constituted by their union : the human 

 soul may, at one and the same instant of time, be created and 

 united with the material principle to form the human individual : 

 but each principle is prior logically* and naturally &quot; prius ratione 

 et natura &quot; : \6ytp r) tyva-et irporepov to that which is constituted 

 by their union. 



Fifthly, the premisses must be better known, or, rather, more 

 knowable or intelligible, than the conclusion. The aim of all in 

 ference is to lead us from the better known to the less known or 

 to the unknown. But demonstration leads us from the real prin 

 ciple or cause to that which proceeds therefrom ; and how can 

 the former be more &quot;known &quot;or &quot;knowable&quot; than the latter? 

 Aristotle explains how this is to be understood, by his famous 

 distinction between the order of nature or reality and the order 

 of our experience : &quot;Prior and more knowable&quot; he writes, 4 &quot; may 

 be understood in two distinct ways : in nature and in our experi 

 ence. What are prior and more familiar_/0r us are what lie nearest 

 to sense- perception ; whereas what are prior and more intelligible 

 simply are the things which lie more remote from sense. Now 



1 MELLONE, op. cit. t p. 252 ; cf. ibid., pp. 258-9. 



2 Cf. ST. THOMAS, Quaestiones Disputatae : De Potentia, xiii. 



3 The &quot; logical &quot; order referred to here is not the order in which our minds 

 acquire knowledge, the order of experience ; it is rather the order in which we under 

 stand things to be related in the real, or natural, or ontological order. Cf. infra, 

 pp. 229, 231-2. 



4 TlpSrfpa 8 iffrl *ol yv&amp;lt;apifj.untpci 8jx&&amp;gt;J ov -yip ra.vr bv irp6r(pov rfj &amp;lt;p&amp;lt;u&amp;lt;rfi icaJ irpbs 

 Tinas irp6Ttpov, oiiSf yixopi/juaTtpov KaJ rifuv yi&amp;gt;&amp;lt;apin&amp;lt;S&amp;gt;Ttpov. Atya&amp;gt; 5 vpbs fipas fiti/ icpArepa 

 KCU yvupifitarepa ra tyyvrfpov rfjr aiffdfio teas, awAccs Si irpdrepa /ca! yvaopifjuartpa. rek 

 iroppanepw. &quot;Effrt 8e iroppondrw /j.fv ret Ka06\ov nd\iffra, tyyvrdrw 8 Tk Kaff ^Kaffra 

 Kol ayrf/ceiTou TOUT dAA.yjA.otJ. Anal. Post., i., cap. ii., 10. Cf. JOSEPH, op. cit., pp. 

 354 sqq. ; WELTON, op. cit., ii., p. 33 ; MERCIER, Logique, pp. 287-90. 



