382 THE PRINCIPLES OF SCIENCE. 



that Aristotle should state the laws of thought, and 

 employ the predicables without implicitly recognising the 

 logical necessity of that method. It is, however, in Por- 

 phyry's remarkable and in many respects excellent ' Intro- 

 duction to the Categories of Aristotle' that we find the 

 most distinct account of it. Porphyry not only fully and 

 accurately describes the Predicables, but incidently intro- 

 duces an example for illustrating those predicables, which 

 constitutes a good specimen of bifurcate classification. 

 Translating his words ^ freely we may say that he takes 

 Substance as the genus to be divided, under which are 

 successively placed as Species Body, Animated Body, 

 Animal, Rational Animal, and Man. Under Man, again, 

 come Socrates, Plato, and other particular men. Now of 

 these notions Substance is the genus generalissimurn, and 

 is a genus only, not a species. Man, on the other hand, 

 is the species specialissima (infima species), and is a species 

 only, not a genus. Body is a species of substance, but a 

 genus of animated body, which, again, is a species of body 

 but a genus of animal. Animal is a species of animated 

 body, but a genus of rational animal, which, again, is 

 a species of animal, but a genus of man. Finally, man 

 is a species of rational animal, but is a species merely 

 and not a genus, being divisible only into particular 

 men. 



Porphyry proceeds at some length to employ his 

 example in further illustration of the predicables. We 

 do not find in Porphyry's own work any scheme or 

 diagram exhibiting this curious specimen of classifi- 

 cation, but some of the earlier commentators and epitome 

 writers drew what has long been called the Tree of 

 Porphyry. 



Thus in the 'Epitome Logica' of Nicephorus Blemmidas, 



Q 'Porphyrii Isagoge,' Caput ii. 24. 



