§ 318. We will first define these terms in the sense in which they are now used, and afterwards examine the principle on which the classification is founded and the sense in which they were originally intended.
(1) A Genus is a larger class containing under it smaller classes. Animal is a genus in relation to man and brute.
(2) A Species is a smaller class contained under a larger one. Man is a species in relation to animal.
(3) Difference is the attribute, or attributes, which distinguish one species from others contained under the same genus. Rationality is the attribute which distinguishes the species, man, from the species, brute.
N.B. The genus and the difference together make up the Definition of
a class-name, or common term.
(4) A Property is an attribute which is not contained in the definition of a term, but which flows from it.
A Generic Property is one which flows from the genus.
A Specific Property is one which flows from the difference.
It is a generic property of man that he is mortal, which is a consequence of his animality. It is a specific property of man that he is progressive, which is a consequence of his rationality.
(5) An Accident is an attribute, which is neither contained in the definition, nor flows from it.