Two Treatises of Government - Book II, Chapter 12 Of the Legislative, Executive, and Federative Power of the Common-wealth
143. THE legislative power is that, which has a right to direct how the force of the common-wealth shall be employed for preserving the community and the members of it. But because those laws which are constantly to be executed, and whose force is always to continue, may be made in a little time; therefore there is no need, that the legislative should be always in being, not having always business to do. And because it may be too great a temptation to human frailty, apt to grasp at power, for the same persons, who have the power of making laws, to have also in their hands the power to execute them, whereby they may exempt themselves from obedience to the laws they make, and suit the law, both in its making, and execution, to their own private advantage, and thereby come to have a distinct interest from the rest of the community, contrary to the end of society and government: therefore in well ordered commonwealths, where the good of the whole is so considered, as it ought, the legislative power is put into the hands of divers persons, who duly assembled, have by themselves, or jointly with others, a power to make laws, which when they have done, being separated again, they are themselves subject to the laws they have made; which is a new and near tie upon them, to take care, that they make them for the public good.
144. But because the laws, that are at once, and in a short time made, have a constant and lasting force, and need a perpetual execution, or an attendance thereunto; therefore it is necessary there should be a power always in being, which should see to the execution of the laws that are made, and remain in force. And thus the legislative and executive power come often to be separated.
145. There is another power in every common-wealth, which one may call natural, because it is that which answers to the power every man naturally had before he entered into society: for though in a common-wealth the members of it are distinct persons still in reference to one another, and as such as governed by the laws of the society; yet in reference to the rest of mankind, they make one body, which is, as every member of it before was, still in the state of nature with the rest of mankind. Hence it is, that the controversies that happen between any man of the society with those that are out of it, are managed by the public; and an injury done to a member of their body, engages the whole in the reparation of it. So that under this consideration, the whole community is one body in the state of nature, in respect of all other states or persons out of its community.
146. This therefore contains the power of war and peace, leagues and alliances, and all the transactions, with all persons and communities without the common-wealth, and may be called federative, if any one pleases. So the thing be understood, I am indifferent as to the name.
147. These two powers, executive and federative, though they be really distinct in themselves, yet one comprehending the execution of the municipal laws of the society within its self, upon all that are parts of it; the other the management of the security and interest of the public without, with all those that it may receive benefit or damage from, yet they are always almost united. And though this federative power in the well or ill management of it be of great moment to the common-wealth, yet it is much less capable to be directed by antecedent, standing, positive laws, than the executive; and so must necessarily be left to the prudence and wisdom of those, whose hands it is in, to be managed for the public good: for the laws that concern subjects one amongst another, being to direct their actions, may well enough precede them. But what is to be done in reference to foreigners, depending much upon their actions, and the variation of designs and interests, must be left in great part to the prudence of those, who have this power committed to them, to be managed by the best of their skill, for the advantage of the common-wealth.
148. Though, as I said, the executive and federative power of every community be really distinct in themselves, yet they are hardly to be separated, and placed at the same time, in the hands of distinct persons: for both of them requiring the force of the society for their exercise, it is almost impracticable to place the force of the common-wealth in distinct, and not subordinate hands; or that the executive and federative power should be placed in persons, that might act separately, whereby the force of the public would be under different commands: which would be apt some time or other to cause disorder and ruin.