Full Idea
The common legal practice is to distinguish three broad categories of excuse: duress, epistemic limitation, and diminished responsibility.
Gist of Idea
Legal excuses are duress, ignorance, and diminished responsibility
Source
Jeff McMahan (Killing in War [2009], 3.2.1)
Book Reference
McMahan,Jeff: 'Killing in War' [OUP 2009], p.116
A Reaction
McMahan cites these with reference to soldiers in wartime, but they have general application. The third one seems particularly open to very wide interpretation. Presumably I can't be excused by just being irresponsible.