Suppose I make a promise to meet a friend for lunch on Friday. By promising, I incur an obligation to meet my friend for lunch. One explanation of why I incur this obligation is that the concept of promising (as well as the action of promising) possesses an essentially normative element. If I make a promise to do such and such, then I have a normative reason to do such and such. If I do not intend to perform a particular action, then I ought not promise to do it -- that is, given that I understand what is involved in promising, I have a normative reason not to promise anything that I do not intend to carry out. If I do keep my promise to meet my friend, the reason for my action can be explained in terms of my having promised to do so. (There is a distinction here between the reason why the two of us are meeting -- to catch up with each other, say goodbye, talk shop, etc. -- and the reason why I carry through with my promise.) My keeping the promise to my friend is guided by the grasp I have of the concept of promising and my understanding of the normative commitment making a promise incurs -- to do what is necessary to keep the promise, barring extenuating circumstances.
Available at: http://works.bepress.com/matthew_pianalto/20/