But though this self-interested commerce of man begins to take place, and to predominate in society, it does not entirely abolish the more generous and noble intercourse of friendship and good offices.  I may still do services to such persons as I love, and am more particularly acquainted with, without any prospect of advantage; and they may make me a return in the same manner, without any view but that of recompensing my past services.  In order, therefore, to distinguish those two different sorts of commerce, the interested and the disinterested, there is a certain form of words invented for the former, by which we bind ourselves to the performance of any action.  This form of words constitutes what we call a promise, which is the sanction of the interested commerce of mankind.  When a man says he promises any thing, he in effect expresses a resolution of performing it; and along with that, by making use of this form of words, subjects himself to the penalty of never being trusted again in case of failure.  A resolution is the natural act of the mind, which promises express:  But were there no more than a resolution in the case, promises would only declare our former motives, and would not create any new motive or obligation.  They are the conventions of men, which create a new motive, when experience has taught us, that human affairs would be conducted much more for mutual advantage, were there certain symbols or signs instituted, by which we might give each, other security of our conduct in any particular incident, After these signs are instituted, whoever uses them is immediately bound by his interest to execute his engagements, and must never expect to be trusted any more, if he refuse to perform what he promised.

Nor is that knowledge, which is requisite to make mankind sensible of this interest in the institution and observance of promises, to be esteemed superior to the capacity of human nature, however savage and uncultivated.  There needs but a very little practice of the world, to make us perceive all these consequences and advantages.  The shortest experience of society discovers them to every mortal; and when each individual perceives the same sense of interest in all his fellows, he immediately performs his part of any contract, as being assured, that they will not be wanting in theirs.  All of them, by concert, enter into a scheme of actions, calculated for common benefit, and agree to be true to their word; nor is there any thing requisite to form this concert or convention, but that every one have a sense of interest in the faithful fulfilling of engagements, and express that sense to other members of the society.  This immediately causes that interest to operate upon them; and interest is the first obligation to the performance of promises.