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The Basic Criteria of Just War Theory; An Introduction

Updated on June 19, 2013

What is just war theory?

Just war theory is applied ethics; it attempts to justify the effects of war as well as determine what is morally acceptable in committing warfare. The criteria for just war theory can be loosely defined in five concepts. Traditionally, however, there is a distinction between the justice of going to war (jus ad bellum) and just conduct in war (jus in bello). Taken together, these factors constitute modern just war theory.*

In recent years, a further distinction, the justice of actions after war (jus post bellum), has been added. For more information on this, see references.

Jus ad bellum

1. Legitimate Authority: war must be declared by competent authority for a public purpose.

2. Just Cause: the avowed cause must be just, all peaceful alternatives must be exhausted, and the means must be proportionate to the just cause.

  • Just cause may include the desire to:
  • protect the innocent from unjust attack;
  • restore rights unjustly denied;
  • re-establish a just order;
  • the requirement of proportionality will be met by:
  • having a sufficient good and just cause that warrants war;
  • weighing the costs as well as the potential for good and evil ends;
  • continuing to weigh the costs throughout the war and including all parties involved;
  • having a reasonable chance of success (unless it is a war of self-defense);

3. Right Intention: Right intention must be had on the part of the just belligerent by:

  • limiting the belligerent to the avowed just cause;
  • requiring the belligerent to always have in mind a just and lasting peace.

Jus in bello

4. Principle of Proportionality: the military means must be proportional to the political and military ends.

  • the military means must be proportionate to discrete and legitimate military ends with the ultimate object of war, the just cause, always in mind;

5. Principle of Discrimination: only legitimate combatants may be targeted by direct attack.

What the pre-war and current warfare distinction means.

This traditional distinction allows for warring parties to be analyzed at multiple levels. A warring party may enter war under just pretenses but wage war unjustly. Warring parties can also enter war under unjust pretenses but fight honorably. This view begins to allow us to make a reasoned and intelligent judgment on the ethics of war.


Why should you care about just war theory?

There are many reasons why one might study just war theory.

If you are in politics, you should have a deep familiarity with just war theory. A statesman may have a direct affect on warfare. A political activist should know just war theory in order to convincingly and intelligently debate the issues of morality in war.

Following closely, if you are a citizen in a democracy, your votes and political sway affect the wars which your nation wages. It is a civic duty to have an inkling on the ethics of war.

As a soldier, you are constantly going to be faced with decisions pertaining to the just conduct of war. While you may not have much choice in many matters of warfare, at sometime in your life you may question whether what you have done or what you will do is just.

Finally, as an ethical person, these matters may directly bear on your life.

References and Links


The Conduct of Just and Limited War, William V. O'Brien.

Just War: Principles and Cases, Richard J. Regan.


The Stanford Encyclopedia of Philosophy entry on War by Brian Orend;

An entertaining guide by the BBC;

You can also check out my hub on an applied case study of the Falklands War.


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    • shalini sharan profile image

      shalini sharan 5 years ago from Delhi

      interesting hub