Harry Frankfurt came up with the idea that the "essence of man lies in will" and how it is important for a person to have second-order volitions. The will is the prime connection between a man's actions and his desires, but reason also plays a role as a tool in sorting through those desires. According to Hume, reason can be an influence, but it can never influence any action of the will. Even though rational thinking through desires could be a faculty that a person could use, the will is the ultimate decider in a person's actions and is truly the basic component of man.
In Freedom of the Will and the Concept of a Person, Frankfurt argues that the essence of a person lies in the particular structure of man called will. This will is the main motivator for one's actions and is constituted by the first-order desires and second-order desires. The first order desires are just basic cravings for an object or an idea-these are desires that even animals possess. What sets apart man from the animal is the formation of second-order desires. Frankfurt states that "It seems to be peculiarly characteristic of humans that they are able to form what I call 'second-order desires' or 'desires of the second order"' (Frankfurt in booklet pg. 16). Second-order desires are a concern about the first-order desires; these are desires for a desire. For example, one might have a first-order desire to smoke marijuana and a second order-desire to desire not to smoke marijuana. These values that one holds could or could not be naturally correct, but they are what reflects what one values as a person. A second-order desire might or might not be a desire that corresponds directly in fulfilling the first-order desire be effective. But when a person wants his first-order desire to happen or to be effective, it becomes his second-order volition or his will. .
Because an action from a specific desire can achieve that specific desire and one has the will or a second-order volition, the problem of choosing which desire should be fulfilled is important to this discussion.