Consent of the governed
An early critic of social contract theory was Rousseau's friend, the philosopher David Hume, who in 1742 published an essay "Of Civil Liberty". The second part of this essay, entitled "Of the Original Contract", stresses that the concept of a "social contract" is a convenient fiction:
As no party, in the present age can well support itself without a philosophical or speculative system of principles annexed to its political or practical one; we accordingly find that each of the factions into which this nation is divided has reared up a fabric of the former kind, in order to protect and cover that scheme of actions which it pursues. ... The one party [defenders of the absolute and divine right of kings, or Tories], by tracing up government to the DEITY, endeavor to render it so sacred and inviolate that it must be little less than sacrilege, however tyrannical it may become, to touch or invade it in the smallest article. The other party [the Whigs, or believers in constitutional monarchy], by founding government altogether on the consent of the PEOPLE suppose that there is a kind of original contract by which the subjects have tacitly reserved the power of resisting their sovereign, whenever they find themselves aggrieved by that authority with which they have for certain purposes voluntarily entrusted him.
— David Hume, "On Civil Liberty"
Hume argued that consent of the governed was the ideal foundation on which a government should rest, but that it had not actually occurred this way in general.
My intention here is not to exclude the consent of the people from being one just foundation of government where it has place. It is surely the best and most sacred of any. I only contend that it has very seldom had place in any degree and never almost in its full extent. And that therefore some other foundation of government must also be admitted.
— Ibid II.XII.20
Natural law and constitutionalism
Legal scholar Randy Barnett has argued that, while presence in the territory of a society may be necessary for consent, this does not constitute consent to all rules the society might make regardless of their content. A second condition of consent is that the rules be consistent with underlying principles of justice and the protection of natural and social rights, and have procedures for effective protection of those rights (or liberties). This has also been discussed by O. A. Brownson, who argued that, in a sense, three "constitutions" are involved: first, the constitution of nature that includes all of what the Founders called "natural law"; second, the constitution of society, an unwritten and commonly understood set of rules for the society formed by a social contract before it establishes a government, by which it does establish the third, a constitution of government. To consent, a necessary condition is that the rules be constitutional in that sense.
Tacit consent
The theory of an implicit social contract holds that by remaining in the territory controlled by some society, which usually has a government, people give consent to join that society and be governed by its government, if any. This consent is what gives legitimacy to such a government.
Explicit consent
The theory of an implicit social contract also goes under the principles of explicit consent. The main difference between tacit consent and explicit consent is that explicit consent is meant to leave no room for misinterpretation. Moreover, you should directly state what it is that you want and the person has to respond in a concise manner that either confirms or denies the proposition.
Voluntarism
According to the will theory of contract, a contract is not presumed valid unless all parties voluntarily agree to it, either tacitly or explicitly, without coercion. Lysander Spooner, a 19th-century lawyer and staunch supporter of a right of contract between individuals, argued in his essay No Treason that a supposed social contract cannot be used to justify governmental actions such as taxation because government will initiate force against anyone who does not wish to enter into such a contract.
Modern Anglo-American law, like European civil law, is based on a will theory of contract, according to which all terms of a contract are binding on the parties because they chose those terms for themselves. Accordingly, it has been argued that social contract theory is more consistent with the contract law of the time of Hobbes and Locke than with the contract law of our time, and that certain features in the social contract which seem anomalous to us, such as the belief that we are bound by a contract formulated by our distant ancestors, would not have seemed as strange to Hobbes' contemporaries as they do to us.
