The right act is the act that a person with good desires would have performed.
Good desires, in turn, are desires that tend to fulfill other desires. For an account of how desires can be evaluated, and the sense in which agents can have motivating reasons to promote and inhibit desires, please see A Harmony of Desires
I am writing a series of posts to show how these propositions explain a number of the elements that we find in this institution we know as 'morality'. In this post, I focus on mens rea or guilty mind.
We typically encounter discussion of 'mens rea' in the philosophy of law. However, it is actually a moral concept. In fact, much of what we encounter in the criminal law actually has a moral foundation. The actions that we seek to make criminal are those actions that are actually immoral – those actions where the people who commit them deserve (in the moral sense) punishment.
Deviations between criminal law and morality are typically categorized as 'unjust' (or 'immoral') law.
Anyway, before a person can be said to deserve punishment the accuser must demonstrate mens rea. That is to say, she must prove not only that the accused committed the act, but that the accused had those mental states that would make him somebody who deserves to be punished.
So, we know that an agent pointed a gun at somebody and pulled the trigger, thus shooting our alleged victim and rendering him dead.
But did he do anything wrong?
We can see that, whatever we are concerned with in making a moral judgment, it is not in the act itself. We can know everything there is to know about the action – the pointing of the gun and pulling the trigger – and not know anything about the guilt of the accused. In order to determine guilt, we need to know why he pulled the trigger.
Let us assume, for a moment, that we discover that the accused had a brain implant, and that the pointing of a gun and pulling the trigger was controlled by somebody else entirely sitting at a key board. In this case, the act cannot even be said to be the accused's action. It is the keyboard operator's action. We don't need to know why the accused pulled the trigger because the accused did not pull the trigger. We need to know why the keyboard operator pressed whatever combination of keys that resulted in the gun firing.
Just as the wrongness of an action does not preside in the specific twitching of muscles that constitute the action itself, it also does not reside in any belief. Perhaps the agent believed that the person he shot was a police officer out to arrest him on an outstanding warrant. In shooting the police officer, we certainly are not arguing that the wrongness of his conduct resides in having this belief.
After all, the statement may be true – and may be something that the prosecutor seeks to get the jury to believe as well. They may well inform the jury, "The victim, in this case, was a police officer who was seeking to arrest the accused on an outstanding warrant." This would be bizarre if the moral culpability rests in having such a belief.
So, if the wrongness is not found in the particular muscle twitching that make up the actions, or in the beliefs of the accused, we really are left with no other option but to seat the moral culpability – the mens rea – in the desires that motivated the action (or the absence of desires that could have prevented it).
We may well understand that the accused wanted to avoid arrest and imprisonment. In fact, punishment is characterized primarily as creating a state that thwarts the desires (directly or indirectly) of the one being punished. It is a way of giving people a reason for action not to perform a crime based on the threat, "If you perform this action (and we catch you), you risk the thwarting of those other desires – and you have motivating reason to act so as to prevent the thwarting of those desires."
Ultimately, the mens rea of criminal law involves demonstrating that the accused had, at the time of the crime, faulty desires. It is not the muscle twitching themselves that we are interested in, or the agent's beliefs. In determining mens rea we are seeking to determine whether the accused had desires people generally have reason to inhibit, or lacked desires that people generally have reason to promote.