In the last four sections of the last chapter (“Of the Dissolution of Government”) of his 2d Treatise on Government: Of Civil Government, John Locke answers the question of “Who should be the judge of whether rulers have overstepped their bounds?” thus: “the body of the people.” John Locke gives an excellent reason for why: rulers are the trustees or deputies of the people.

John Locke also poses and answers another hard question: What if a ruler refuses to be judged by the people? He says that if a ruler refuses to be judged by the people, then anyone who judges that a ruler has overstepped his or her bounds may consider themself to be at war with that ruler. I think John Locke would consider this provision not to apply in a democracy in which regular free elections can topple a ruler.

§. 240. Here, it is like, the common question will be made, Who shall be judge, whether the prince or legislative act contrary to their trust? This, perhaps ill-affected and factious men may spread amongst the people, when the prince only makes use of his due prerogative. To this I reply, The people shall be judge; for who shall be judge whether his trustee or deputy acts well, and according to the trust reposed in him, but he who deputes him, and must, by having deputed him, have still a power to discard him, when he fails in his trust? If this be reasonable in particular cases of private men, why should it be otherwise in that of the greatest moment, where the welfare of millions is concerned, and also where the evil, if not prevented, is greater, and the redress very difficult, dear, and dangerous?

§. 241. But farther, this question, (Who shall be judge?) cannot mean, that there is no judge at all: for where there is no judicature on earth, to decide controversies amongst men, God in heaven is judge. He alone, it is true, is judge of the right. But every man is judge for himself, as in all other cases, so in this whether another hath put himself into a state of war with him, and whether he should appeal to the Supreme Judge, as Jephtha did.

§. 242. If a controversy arise betwixt a prince and some of the people, in a matter where the law is silent, or doubtful, and the thing be of great consequence, I should think the proper umpire, in such a case, should be the body of the people: for in cases where the prince hath a trust reposed in him, and is dispensed from the common ordinary rules of the law; there, if any men find themselves aggrieved, and think the prince acts contrary to, or beyond that trust, who so proper to judge as the body of the people, (who, at first, lodged that trust in him) how far they meant it should extend? But if the prince, or whoever they be in the administration, decline that way of determination, the appeal then lies no where but to heaven; force between either persons, who have no known superior on earth, or which permits no appeal to a judge on earth, being properly a state of war, wherein the appeal lies only to heaven; and in that state the injured party must judge for himself, when he will think fit to make use of that appeal, and put himself upon it.

In very last section of his 2d Treatise on Government: Of Civil Government John Locke declares himself a constitutionalist in the sense that once a form of government is in place that sets proper bounds on rulers, the constitutional forms already established must be followed, except “when by the miscarriages of those in authority it is forfeited.”

§. 243. To conclude, The power that every individual gave the society, when he entered into it, can never revert to the individuals again, as long as the society lasts, but will always remain in the community; because without this there can be no community, no commonwealth, which is contrary to the original agreement: so also when the society hath placed the legislative in any assembly of men, to continue in them and their successors, with direction and authority for providing such successors, the legislative can never revert to the people whilst that government lasts; because having provided a legislative with power to continue for ever, they have given up their political power to the legislative, and cannot resume it. But if they have set limits to the duration of their legislative, and made this supreme power in any person, or assembly, only temporary; or else, when by the miscarriages of those in authority it is forfeited; upon the forfeiture, or at the determination of the time set, it reverts to the society, and the people have a right to act as supreme, and continue the legislative in themselves; or erect a new form, or under the old form place it in new hands, as they think good.

Throughout his 2d Treatise on Government: Of Civil Government John Locke is insistent that rulers, too, are subject to the rule of law. And the rule of civil law is in turn subject to the preexisting law of nature.

For links to other John Locke posts, see these John Locke aggregator posts: 

• John Locke's State of Nature and State of War

• On the Achilles Heel of John Locke's Second Treatise: Slavery and Land Ownership

• John Locke Against Natural Hierarchy

• John Locke's Argument for Limited Government