The ethics of warfare: Is it ever morally right to kill on a massive scale


War has been puzzling philosophers for centuries, and it isn’t hard to see why. What could be more intuitive or ethical than the belief that it is morally wrong to kill on a massive scale?

However, many would argue that there are times when war is morally permissible, and even obligatory. The most famous way of ethically assessing war is to use ‘Just War Theory’; a tradition going back to St. Augustine in the 5th Century and St. Thomas in the 13th Century. Just War theory considers the reasons for going to war (Jus ad bellum) and the conduct of war (Jus in bello). This distinction is important. A war might be ethical but the means unethical, for instance, using landmines, torture, chemicals and current debate is concerned with drones.

Just War theory sets out principles for a war to be ethical. The war must be:

  • Waged by a legitimate authority (usually interpreted as states)
  • In a just cause
  • Waged with right intention
  • Have a strong probability of success
  • Be a last resort
  • Be proportional

In addition, there are three principles for conduct in war:

  • Discrimination (distinguishing between enemy combatants and non-combatants)
  • Proportionality (the harms must be proportional to the gains)
  • Actions must be militarily necessary

When attempting to apply and interpret these principles considerable disagreement arises, as evidenced by the – still ongoing – debate about the 2003 US-led invasion of Iraq. Just war principles are used to address the question of whether the war lacked legitimate authority without a UN Resolution.

Legitimate authority is at issue in all conflicts, including those considered to be acts of terrorism or insurgency. Think about recent uprisings such as the 2011 ousting of Gaddafi's regime in Libya and the other movements loosely termed the Arab Spring; and most timely the current debate about whether to arm the ‘rebels’ in Syria. Are these legitimate authorities? And does legitimate authority make sense anymore?

Establishing ‘just cause’ is also problematic, for example, self-defence is widely recognised, and the UN Charter grants states a right to defend themselves. However, other ‘just causes’ are more difficult to defend. Particularly controversial is humanitarian intervention, even though it is sometimes seen as obligatory and indeed, the most ethical reason for war. It was for humanitarian reasons that NATO intervened in Kosovo in 1999, but, there are other instances where humanitarian disasters are left (perhaps most controversially the failure to intervene in the Rwandan genocide in 1994).

All criteria are problematic and hard to meet. Think about ‘right intention’ with regard to the 2003 Iraq war and discussions about the ‘real’ motives of Bush and Blair. And when we come to proportionality, the contemporary debate is particularly fraught. Can it ever be proportional to use drones where there is no risk to life on one side and risk to many lives (including civilian lives) on the other? And when battles are fought in villages and homes by those with no uniforms, how can the principle of discrimination ever be respected – and indeed should it be?

The character of war is changing fast and the ethics needs to keep pace with that change. These particular principles might well need revision. But we should not imagine the fundamental ethical issues have changed. It is still the case that in a sense war is inherently unethical. To be justified, significant ethical reasons are required and although imperfect Just War theory continues to be one way to seek such reasons.

Heather Widdows, Professor of Global Ethics, Department of Philosophy, Co-Leader of Saving Humans IAS theme