 Afterwards a sentiment of morals concurs with interest, and becomes a new obligation upon mankind. This sentiment of morality, in the performance of promises, arises from the same principles as that in the abstinence from the property of others. Public interest, education, and the artifices of politicians, have the same effect in both cases. The difficulties, that occur to us, in supposing a moral obligation to attend promises, we either surmount or elude. (Treatise, 3.2.5)