A division has emerged in the self-defence literature between those who hold what I will call internalist accounts of liability, and those who hold what I will call externalist accounts of liability.  Internalists think that one can be liable to harm on grounds of defence only when those harms are necessary for avoiding or averting a threat.  Externalists think that one can be liable to harm on grounds of defence even if the harm is not necessary for averting a threat.

I argue that a harm can count as defensive only if it is a means of averting a threat. Given this, an account of liability to defensive harm can justify the infliction only of harms that are means of averting threats.  This undermines purely externalist views.  I suggest that if there is a genuine rival to the internalist account, it is what I will call the proportionate means account of liability to defensive harm.  The proportionate means account is externalist because it holds a person liable to defensive harm on the grounds of their moral responsibility for an unjust threat. However, the proportionate means account takes seriously that this is liability to defensive harm, and that this must mean only harm that is capable of defending a person or some other good such as property. A use of force might not be the least harmful means of averting a threat, but it must be a means of averting a threat to count as defensive.  Like internalism, this account must be supplemented if it is to plausibly explain liability to harm in a range of cases. I explore what these additional justifications for harming might be, and briefly consider why it may be impermissible for an attacker to defend himself against a harm to which he is not liable.

I do not argue in favour of either internalism or the proportionate means account here. Rather, I explain what these accounts can do and what they cannot do, and sketch how a defender of either will need to proceed in order to capture the range of cases that we want to be able to explain.


Helen Frowe is, from november, Wallenberg Academy Research Fellow at Stockholm University.

Helen Frowe, personal page.