In every government there are three sorts of power: the legislative; the executive in respect to things dependent on the law of nations; and the exec… - Montesquieu

" "

In every government there are three sorts of power: the legislative; the executive in respect to things dependent on the law of nations; and the executive in regard to matters that depend on the civil law.
By virtue of the first, the prince or magistrate enacts temporary or perpetual laws, and amends or abrogates those that have been already enacted. By the second, he makes peace or war, sends or receives embassies, establishes the public security, and provides against invasions. By the third, he punishes criminals, or determines the disputes that arise between individuals. The latter we shall call the judiciary power, and the other, simply, the executive power of the state.
When the legislative and executive powers are united in the same person, or in the same body of magistrates, there can be no liberty; because apprehensions may arise, lest the same monarch or senate should enact tyrannical laws, to execute them in a tyrannical manner.
Again, there 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.
There would be an end of every thing, were the same man, or the same body, whether of the nobles or of the people, to exercise those three powers, that of enacting laws, that of executing the public resolutions, and of trying the causes of individuals.
The executive power ought to be in the hands of a monarch, because this branch of government, having need of dispatch, is better administered by one than by many: on the other hand, whatever depends on the legislative power, is oftentimes better regulated by many than by a single person.
But, if there were no monarch, and the executive power should be committed to a certain number of persons, selected from the legislative body, there would be an end of liberty, by reason the two powers would be united; as the same persons would sometimes possess, and would be always able to possess, a share in both.