Self-defense against the initiation of force is generally accepted, though not always advocated, in most systems of morality. My book “Universally Preferable Behavior: A Rational Proof of Secular Ethics” touched on general aspects of self-defense, which I would like to expand upon here.

Generally speaking, self-defense is the ability to use proportional violence to avoid or minimize harm to oneself during an unprovoked attack. The phrase thus generally refers to the use of violence, rather than merely escaping a violent situation, and so, in the UPB framework, must be subject to moral evaluation, rather than a neutral or aesthetic (APA) evaluation.

The first thing to recognize about self-defense is that although it describes the use of violence, it remains fundamentally different from the initiation of force, in that it is reactive, rather than proactive violence. Self-defense, then, does not exist in the absence of the initiation of force. In other words, self-defense is a potential effect of the initiation of force, and thus the primary moral evaluation must be focused on the initiation of force, which is discussed in great detail in “Universally Preferable Behavior: A Rational Proof of Secular Ethics.”

A second aspect of self-defense is that it covers far more than physical attacks from other people. Few people would object to a man hitting an attacking bear or shark on the nose, or taking antibiotics to kill off an infection, or having a swollen appendix or rotten tooth removed. These can all be considered categories of self-defense, in that force (and poison against bacteria) is used to defend the body against an imminent and growing physical danger or attack. If self-defense is morally invalid, then all these actions would be very hard to justify. This does not constitute an ironclad proof of the validity of self-defense, but it does indicate that opposing self-defense creates insurmountable practical obstacles.

Three Possibilities

Using the UPB framework, there are three main possibilities to consider when evaluating moral propositions regarding self-defense:.

1. Self-defense is morally permissible.

2. Self-defense is morally required.

3. Self-defense is morally prohibited.

In the first instance, self-defense is morally permissible, but it is not immoral to refrain from defending yourself. In the second instance, self-defense is morally required – and thus, as proved in the UPB book, violence can be used against those who do not defend themselves. In the third instance, self-defense is morally prohibited, and thus violence can be used against those who do defend themselves.

Common sense draws us towards the first instance – that self-defense is morally permissible, but not morally required – but let us discuss this possibility last, because if we have disposed of the other two options, this first one becomes much more credible.

Self-Defense Is Morally Prohibited

If self-defense is morally prohibited, then the UPB-compliant moral statement would be something like this:

“It is universally preferable for all people at all times and in all locations to refrain from defending themselves against attack.”

This proposition falls apart very quickly. First of all, since that which is universally banned may be subject to violent opposition, then the initiation of violence cannot be universally banned, since self-defense is also universally banned. However, the arguments in the UPB book clearly demonstrate that the initiation of force cannot be universally preferred, and therefore self-defense cannot be invalid.

Secondly, to ban self-defense is to ban the effect of an action (the initiation of force), but not the action itself. This is like banning murder, but not killing, or to argue that making someone fall off a cliff is immoral, but pushing them off a cliff is moral. You cannot have a shadow without an object and a light source, and neither can the effects of an action be immoral, but that action which causes it be moral. Thus self-defense cannot be immoral, while the initiation of force is moral. But if the initiation of force is immoral, then self-defense is justified, again, as described in “Universally Preferable Behavior: A Rational Proof of Secular Ethics.”

Thirdly, if self-defense is immoral, then violence can be used against somebody acting in self-defense. However, by definition someone acting in self-defense is already subject to violence – that of the attacker. However, the UPB framework clearly demonstrates that the initiation of violence is immoral – if self-defense is also immoral, then a man acting in self-defense can be aggressed against – which is already happening. In other words, the same action -- aggression against a man -- becomes both immoral and moral at the same time. It is immoral because the initiation of force is wrong, but it is moral because using force against a man acting in self-defense is moral.

These logical impossibilities and contradictions – not to mention the practical impossibilities of acting in accordance with such illogical rules – clearly refute the proposition that self-defense is morally prohibited.

Self-Defense Is Morally Required

Perhaps self-defense is morally required – this seems closer to the truth, but also feels problematic, to say the least. In the UPB framework, the non-initiation of force is morally required, which is to say that the non-initiation of force avoids immorality.

If a certain action is morally required, then the opposite action must be morally banned, and thus subject to restraining force. Since the non-initiation of force is morally required, the opposite action – i.e. the initiation of force – may then be subject to restraining force, i.e. self-defense.

However, if self-defense is morally required, then refraining from defending yourself must be morally evil, and thus subject to restraining force. However, we then run into the same logical contradiction outlined above. If Bob attacks Doug, and Doug is morally required to defend himself, but refrains to defend himself, then Bob's attack becomes morally justified, since Doug is acting in an evil manner by avoiding self-defense. However, the same attack cannot be magically transformed from evil into good, and thus self-defense cannot be morally required, since it would thus transform an evil action – the initiation of force – into a virtuous action, which would be the just punishment of defenselessness.

Furthermore, if self-defense is morally required, then any action taken – or avoided -- which brings harm to a person would justify a violent attack against him or her. I think most of us would be fairly uncomfortable with the idea of violently attacking the overweight, or those who do not get regular medical checkups, or take antibiotics for an infection, or get a rotten tooth pulled and so on.

Lastly, as discussed in the UPB book, a good rule of thumb regarding moral propositions is the “coma test,” which states that a man in a coma cannot be rationally accused of moral evil. Clearly, a comatose man cannot act in self-defense, which further supports the rational and empirical objections against the proposition that self-defense is morally required.

Self-Defense Is Morally Permissible

The elimination of the other two major possibilities lends strong support to the proposition that self-defense is morally permissible, but not required. This rule allows us to use force to defend against the initiation of violence, but does not support the use of force against us if we either do not or cannot use force in self-defense. It also accords with the medical reality that to undergo surgery to remove an inflamed appendix is not immoral, but neither is it immoral to avoid such a surgery – in other words, self-defense even against a dangerous organ is permissible, but not required.

Since self-defense is morally permissible, we may not use force against someone engaged in an active defense against an attack – in other words, we may not morally join in with the attacker. This restriction helps us avoid the logical impossibility of defining an attack as immoral, while our simultaneous attack becomes magically moral.

Since self-defense is a universal standard, it is not restricted to a single individual – i.e. the individual being attacked – but extends to everyone, thus permitting third-party defense such as security guards and courageous bystanders. (It also validates the highly useful proposition that it is preferable for a skilled third party to take out my appendix rather than forcing me to do it myself.)

Since self-defense is a reactive action, it can be universalized, since it is merely the shadow of the action of the initiation of force – where the initiation of force is not present, neither will self-defense be present. Any reasonable moralist would far prefer the non-initiation of force to self-defense, just as any sane person prefers not getting sick to getting cured. The initiation of force mathematically adds to the amount of violence in the world, while self-defense does quite the opposite, and even from this utilitarian standpoint, a lot of good is done through the moral permissibility of self-defense.

In summary, then, UPB validates the proposition that self-defense is morally permissible, but not required, which accords with our commonsense notions of morality, and with the logical rigor and strictness required by the approach of Universally Preferable Behavior.