Aristotle - The Organon - index for TOPICA Book 4 Part 1

Species are distinguished by essential properties

Paragraph 1 Next we must go on to examine questions relating to Genus and Property.
Paragraph 2 Especially you should take a look at the definition of Accident, and see whether it fits the genus mentioned, as (e.g.) is also the case in the instances just given.
Paragraph 3 Moreover, see whether the genus and the species be not found in the same division, but the one be a substance while the other is a quality, or the one be a relative while the other is a quality, as (e.g.) 'slow' and 'swan' are each a substance, while 'white' is not a substance but a quality, so that 'white' is not the genus either of 'snow' or of 'swan'.
Paragraph 4 Again, see whether it be necessary or possible for the genus to partake of the object which has been placed in the genus.
Paragraph 5 Moreover, see if there be anything of which the species rendered is true, while the genus is not so, e.g. supposing 'being' or 'object of knowledge' were stated to be the genus of 'object of opinion'.
Paragraph 6 Again, see whether the object placed in the genus be quite unable to partake of any of its species:
Paragraph 7 Moreover, see if the term placed in the genus has a wider denotation than the genus, as (e.g.) 'object of opinion' has, as compared with 'being':
Paragraph 8 See also whether the genus mentioned fails, or might be generally thought to fail, to apply to some object which is not specifically different from the thing in question;

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