Conditions for a 'Just War'

By Paul Noceja

Brief summary

The ‘Just War Theory’ is a Christian belief that seeks to establish the fact that a war can be justified and limited. Derived from the concepts first identified by St Thomas Aquinas, the conditions of a just war are therefore in the context of medieval-type wars.


St Augustine wrote two of the five criteria for a Just War. However, Aquinas is considered the writer and adding clarity and philosophy to the elements. Aquinas also contributed the third principle. Furthermore, Christian philosophers debated on the theory and eventually compounded five rules.

The five principles

  1. The war must be started and controlled by the state and/or its ruler such as a King. This is also called the legitimate ruling authority.
  2. A just cause must be established with a chance of winning.
  3. War must be a last resort after all other options have been exhausted and have a good chance of success.
  4. The war should promote good and overcome evil. Peace and justice must be restored quickly.
  5. Proportionality - only enough force should be applied, enough to attain peace. Innocent civilians should not be harmed.

References