A member of the studio audience objects,
It is not accurate to maintain that "desires are the only reasons for action that exist." Rather, desires are the only reasons for action that exist for the person with those desires.
My original description is accurate.
I would hope that, if I were to say that natural causes are the only causes that exist, I would not be accused of saying that each individual effect is the result of every cause that exists. Rather, the reader should assume that there is still something further to be said about the various relationships between different causes and different effects.
Similarly, my statement that desires are the only reasons for action that exist should not be taken to mean that each individual action is the result of every desire that exists. Rather, the reader should still allow that there is more to be said about the relationships between different actions and different desires.
Desirism also contains the following two claims.
Each person acts so as to fulfill the most and strongest of her own desires given her beliefs
Each person seeks to act so as to fulfill the most and strongest of her own desires.
One of the implications of this is that false and incomplete beliefs will put at risk a person attempts to fulfill the most and strongest of her desires. This is why we have a reason to condemn lying and other forms of deception. Liars, I argue, are parasites who infect a brain with false beliefs. These false beliefs then cause the infected agent to act in ways that often thwart the desires of the agent, but fulfill the desires of the liar.
It is because agents act so as to fulfill the most and strongest of their own desires, given their beliefs, that each of us has reasons to be concerned with what other people desire. I have reason to promote an aversion to taking the property of others without consent because I do not want others walking away with my property.
To whatever degree people have an aversion to taking the property of others without consent, then to that degree I do not need to worry as much about other people walking away with my stuff. The fact that they will act to as to fulfill the most and strongest desires given their beliefs will include the fact that they will act so as to fulfill their desire not to walk away with other peoples' stuff without their consent. That means I have to worry less about others walking away with my property.
If, on the other hand, every desire was a reason for every single action, then we would never have to worry about morality. Each act would, in fact, be caused by every single desire that exists regardless of whose it is, and would automatically go to fulfill the most and strongest of all desires that exist. I would not need to worry about the desires that you had and how they may measure up against desires that exist because these two sets would be identical.
That's simple nonsense.
A desire counts as a reason only for the agent that has the desire.
Yet, it is still true - and remains true - that desires are the only reasons for action that exist. No person has a reason for action that exists that is something other than a desire. If you know of something that is not a desire, but is still a reason for action that exists, then please point it out to me. I hold that there is no such entity. That is precisely what I mean when I say that desires are the only reasons that exist.
This is true in the same sense that, if you know of a cause that exists that is supernatural rather than natural, I challenge you to point it out to me. I hold that there is no such entity. That is precisely what I mean when I say that natural causes are the only causs that exist.