  But, Hume argues, it is absurd to think that one can actually bring an obligation into existence by willing to be obligated. What makes an action obligatory is that its omission is disapproved by unbiased observers. But no act of will within an agent can directly change a previously neutral act into one that provokes moral disapproval in observers (even in the agent herself). Sentiments are not subject to such voluntary control. Even on a moral rationalist view the thesis would be  absurd: to create a new obligation would be to change the abstract relations in which actions and persons stand to one another, and one cannot do this  by performing in one’s own mind an act of willing such a relation to exist. Thus, there is no such act of the mind. Even if people in their natural (pre-conventional) condition “cou’d perceive each other’s thoughts by intuition,” they could not understand one another to bind themselves by any act of promising, and could not be obligated thereby. Since the necessary condition for a natural obligation of promises cannot be fulfilled, we may conclude that this obligation is instead the product of group invention to serve the interests of society.