As noted, judicial functions and powers were intermixed with legislative and executive powers in both England and in the colonies, notwithstanding Blackstone’s call for at least a measure of judicial independence. In 1748, the French lawyer Charles-Louis de Secondat, Baron de LaBrede et de Montesquieu, commonly known simply as Montesquieu, published The Spirit of the Laws, a book that would have a profound impact on the development of the theory of separation of powers in the United States. Like Locke, Montesquieu published his work anonymously because his ideas, too, were considered radical.
Montesquieu joined Blackstone in focusing on the requirements for political liberty. Political liberty required devising ways to prevent the abuse of governmental power. How, he asked, can government be organized so that “no man need be afraid of another”? His response was that government must be constituted so that “no man shall be compelled to things to which the law does not oblige him, nor forced to abstain from things which the law permits.” How a particular government is best constituted to achieve this goal, he argued, depended in large part on the social, economic, and geographic conditions of the society.
No man shall be compelled to things to which the law does not oblige him, nor forced to abstain from things which the law permits.”Montesquieu
Montesquieu admired the British constitution as a model of a mixed constitution. That is, all three classes—monarchy, aristocracy, and commoners—played an important governing role in the constitutional system. Montesquieu identified two institutions primarily responsible for exercising governmental power: legislative and executive. One part of the executive focused on domestic or civil matters, and one part focused on foreign relations or the law of nations. However, Montesquieu also recognized the existence of a “judiciary power.” Political liberty, he argued, requires that the judiciary power be separated from the legislative and from the executive:
. . .[T]here is no liberty, if the judiciary power be not separated from the legislative and executive. Were it joined with the legislative, the life and liberty of the subject would be exposed to arbitrary control; for the judge would be then the legislator. Were it joined to the executive power, the judge might behave with violence and oppression.
Unlike Blackstone, however, Montesquieu did not believe that the judiciary power should be exercised by a judicial branch of government. Instead, the responsibility to judge whether laws have been broken “should be exercised by persons taken from the body of the people at certain times of the year, and consistently with a form and manner prescribed by law, in order to erect a tribunal that should last only so long as necessity requires.” The judgments of these tribunals ought to be fixed, but the tribunals themselves “ought not be fixed.” In this way, Montesquieu believed, the judging power, “so terrible to mankind,” is for all practical purposes made “invisible.”