The Six Books of the Commonwealth
In the earlier part of the Six books of the Commonwealth when he is discussing the commonwealth as such, he not infrequently uses the term 'natural justice', without however explaining what he meant by it. The context generally suggests however that he meant respect for the rights of the subject to his liberty and property. In this last chapter on the other hand it is political justice and not natural that he is talking about. He had noticed the difference when he observed that Plato thought of justice as a philosopher and not as a jurist. In this last chapter Bodin is speaking as a jurist. He defines it in legal terms, as the principle upon which rewards and punishments are distributed in the commonwealth, that is to say the working of the criminal law, and the administration. But whereas natural justice is presumably in his view constant and universal, here the proper order of justice is relative to the type of commonwealth.
Commutative justice, or the strictly equal distribution of honours and penalties preserves a democracy but would destroy an aristocracy. Conversely distributive justice, or award in accordance with the quality of persons, safeguards an aristocracy but would corrupt a democracy. In a monarchy where a more elastic social system is possible than in either of the other two types, since in it classes are at once distinguished and yet not mutually exclusive, harmonic justice is the appropriate form since by it honours are given not in accordance with the status of persons, but with their particular suitability.
The Spirit of Laws
Montesquieu spent nearly twenty years researching and writing De l'esprit des lois (The Spirit of the Laws), covering a wide range of topics in politics, the law, sociology, and anthropology and providing more than 3,000 citations. In this political treatise Montesquieu advocates constitutionalism and the separation of powers, the abolition of slavery, the preservation of civil liberties and the rule of law, and the idea that political and legal institutions ought to reflect the social and geographical character of each particular community.
In its classification of kinds of political systems, Montesquieu defines three main kinds: republican, monarchicl, and despotic. As he classifies them, Republican political systems vary depending on how broadly they extend citizenship rights -- those that extend citizenship relatively broadly are termed democratic republics, while those that restrict citizenship more narrowly are termed aristocratic republics. The distinction between monarchy and despotism hinges on whether or not "intermediate powers" (such as the nobility, the clergy, etc.) exist that can restrain the authority of the ruler: if so, the regime counts as a monarchy; if not, it counts as a despotism.
Driving each classification of political system, according to Montesquieu, must be what he calls a "principle". This principle acts as a spring or motor to motivate behavior on the part of the citizens in ways that will tend to support that regime and make it function smoothly. For democracies (and to a somewhat lesser extent - for republics), this spring is the love of virtue -- the willingness to put the interests of the community ahead of private interests. For monarchies, the spring is the love of honor -- the desire to attain greater rank and privilege. Finally, for despotisms, the spring is the fear of the ruler. A political system cannot last if its appropriate principle is lacking. Montesquieu claims, for example, that the English failed to establish a republic after the Civil War (1642–1651) because the society lacked the (democratic) requisite: the love of virtue.