We must not expect to find in the last three Books of the Politics a systematic description of the various forms of constitution dealt with in them and a complete estimate of their strength and weakness, their merits and defects. The object of these Books is rather a practical object, to teach statesmen how to frame, amend, and administer each constitution so that it may last. Aristotle is naturally led in the course of his inquiries on this subject to mark off the various forms and sub-forms of constitution from each other, and incidentally to throw much light on their nature and tendencies, but his paramount object is a practical object, to give guidance to statesmen, not to set before us a detailed picture of each constitution and its working. We gather from what he tells us that statesmen were not aware how many sub-forms of each constitution existed, and that consequently they committed errors both in introducing and in amending constitutions. They probably confounded the sub-forms, and gave one of them institutions appropriate to another. We gather also that they often introduced constitutions and sub-forms of constitution where they were out of place; that they often sought rather to make the constitutions they framed pronounced examples of their type than to make them durable; and that they commonly did not attempt to create by education and habituation an êthos favourable to the maintenance of the constitution. Aristotle seeks to enable statesmen to avoid all these errors. His object is to make the study of constitutions more thorough and detailed and more practically useful than it had been.

A few remarks may here be added to what has already been said in vol. i. p. 521 sqq. as to the teaching of this Book.

If we study the eleven causes of στάσις and constitutional change enumerated in c. 2. 1302 a 34 sqq. (see vol. i. p. 523 sqq.), we shall see that they may be grouped under three main heads. Στάσις and constitutional change may arise either from a certain emotional state of the minds of the citizens or some of them, or from social causes, such as the increase of a class in size out of proportion to the rest or the unlikeness of one part of the citizen-body to the other, or from negligence on the part of the authorities of the State and similar causes. It is obvious that a great difference exists between the second group of causes and the two others. Negligence in government can be avoided, and it is possible also to avoid arousing feelings of envy, or contempt, or indignation at oppression or fears of future oppression, but it is far less easy to prevent a class increasing in size or credit, or an individual or individuals acquiring a pre-eminence in power, or to secure the existence of a midway class capable of holding the balance between rich and poor, or to soften distinctions of race or geographical contrasts.