The basis of classification which Aristotle uses for political
problems may be compared to that of the classification of biological
problems in the History of Animals. In biology a double
classification is used to set forth difficulties and to classify
phenomena, a classification of animals combined with a classification
of the parts of animals.In politics too a double classification
is introduced once the doctrines of predecessors and
the examples of good states have been dismissed in Book II
classification of states and of the classes of citizens which form
the parts of states.