called the contractarian ‘principle of defeasibility’, and would seem to be an essential component of any successful contractarian account. The motivation for it has already been discussed: the implementation of the social contract will itself open up the possibility of a new kind of danger that the bargainers never confronted in the state of nature: the threat of free-riders. Hence, in their formulation of the contract, the bargainers will have reason not only to adopt principles that will minimize the evils they encounter in the state of nature, but they will also have reason to adopt a further clause that would seek to minimize the dangers uniquely presented by the implementation of the contract. Roughly stated, the ‘defeasibility principle’ would sanction exceptions to restrictions precisely insofar as those same restrictions are being exploited by free-riders seeking to further their own advantage at the expense of the rest of the constraint-abiding population. To the extent that a free-rider is breaking a restriction and violating an innocent person, a restriction may be overridden if doing so is necessary for the protection of the innocent, or to prevent the free-rider from succeeding in his efforts to profit at the expense of the moral system. One might put the same point by saying that “protection under the contract is conditional on conformity with the contract,”18 and that the extent to which someone breaks the contract in pursuit of personal gain is the extent to which he forfeits his rights against others that they continue to adhere to the rules of the contract when dealing with him.
Self-defense, of course, provides a concrete illustration of this: restrictions against harming others are agreed to because, in the long run, they serve everybody’s greater good. However, a free-rider should not expect his fellows to remain committed to these restrictions while he breaks them in an effort to achieve undue gain; the contractarian principle of defeasibility will permit the intended victims of the free-rider’s offense to override the restriction if doing so is a necessary means to protecting themselves from the free-rider’s violations.
This, then, is the way restrictions and their principled exceptions arise out of the bargainers’ self-interest-maximizing motive. But our task is not done. For as we noted above, we must be sure that whatever rules our bargainers agree to fit both dimensions of
Kagan 1989, p. 135