Handbook of the History of Logic: - Fordham University Faculty

The Assimilation of Aristotelian and Arabic Logic up to the Later Thirteenth Century 323
Figure 4. The Porphyrian Tree
from something else by an separable accident, like Socrates sitting differs from
Socrates standing. A proper difference is the difference between things through an
inseparable accident, like ‘snub nosed’. Finally, a most proper difference is when
something differs from something else by a specific difference, like humans differ
from horses by rationality. This is of course the most important notion if difference.
A difference of this kind is, furthermore, both dividing and constitutive,
since it divides the genus and is the constitutive part of the species. The genus
‘animal’ is divided by ‘rational’ and ‘rational’ is what constitutes the species ‘human
being’. This is an identical treatment to what we saw above in Averroes’
commentaries (section 3.2).
A property (proprium) is always associated with every individual belonging to a
given species, as for example ‘being able to laugh’ is always associated with every
human being. Although a human being does not always laugh, it will always be
able to. If there are humans then there will also be the property, ‘able to laugh’.
An accident is something which can be in a subject and missing from a subject
without its corruption, like white, black, and sitting. Accidents can, however,
be separable and inseparable. An inseparable accident is an accident which as a
matter of fact is never separated from its subject, like the blackness of an Etiopian
(the example stems from Porphyry himself).
Based on these some similarities and differences between the predicables are
usually observed. One major difference between the first four and accidents is
that genus, species, differentia and property all are either in the thing they are
predicated of or not, that is, they either participate fully or not at all in the subject