A person can only do an unjust or just act if they do so voluntarily.
If you do an unjust act involuntarily (check out Aristotle's definition of this), you might be blamed—but not considered 100% unjust.
A quick recap of involuntary action: 1) when a person acts in ignorance; 2) when the action is not his choice; 3) when the action is forced.
There are also incidental actions—things we do not intend to be just or unjust, but they end up being so.
Aristotle says that what is voluntary is something deliberated on beforehand.
He includes as involuntary the things we do in ignorance and under ignorance.
These are three: 1) when a person doesn't realize that he'll cause harm or use a harmful instrument; 2) when the action isn't aimed at a particular person; 3) the "end" is unexpected.
If in any of these cases, the person involuntarily acts unjustly and causes harm—it isn't what he intended. This can only be called error.
If there's pre-meditation (i.e. deliberation), then the act is properly unjust. And if we harm someone intentionally but without deliberation, it's still unjust.
But if these acts of injustice don't come about because of wickedness and conscious choice, the doer is not an unjust person.
Aristotle says that in matters of judgment, it's not the result that we dispute. If there's a body lying on the ground in a pool of blood, we pretty much know that we've got a violent death.
The real thing at issue is who is at fault. What is the just action that will set things right?
When a person harms by choice, he behaves unjustly. And when that person seeks to gain more of anything through an unjust act, he actually becomes unjust.
On the other side of the spectrum, a person may be called just if he performs just acts voluntarily.
Aristotle addresses forgiveness as well. We can forgive involuntary things (or not).
If they are done without understanding, they might be forgiven. If done in a "passion," they might not be forgiven.