The Need to Attend to Probabilities (for Purposes of Self-Defense and Other Preemptive Actions)

In this short essay I ask what must someone acting in defense of others believe and with what level of credence in order not to be culpable for so acting. I focus on defense of others to avoid the issue of excuse, as the defender of others is not acting out of fear for his own safety, a fear that might excuse the defensive acts of the victim of the feared attack. I focus on beliefs and levels of credence because no defender can know for certain the factors relevant to permissible defensive actions.