The Principles of Proportionality and Precautions

Built upon the rule of limited warfare and principle of distinction, these principles contribute to the composition of customary international law.

The principles of proportionality and precautions further restrict the means and methods of warfare in order to spare the civilian population from the consequences of war.

Principle of Proportionality

A lawful attack against a military objective or combatant must always be proportionate to the aim it seeks to accomplish in relation to the possible consequential civilian damage.

Article 51, paragraph 5 of Additional Protocol I prohibits the attacks which may be expected to cause incidental loss of civilian life, injury to civilians, and damage to civilian objects - this would be considered excessive in relation to the concrete and direct military advantage anticipated, according to IHL.

The damage caused to civilians by a military attack must never be excessive, and is referred to as collateral damage.

When is collateral damage considered to be excessive?

There is no objective threshold provided by IHL, such as a specified number of affected civilian victims to constitute as 'excessive' collateral damage. Instead, the job is left to the reasonable commander on the ground who must make a judgement based upon the circumstances ruling at the time.

IHL does however provide a number of guidelines due to the subjective nature of this judgement. It is provided that a military advantage gained by an attack must be concrete and direct as opposed to hypothetical, and must result from a specific operation rather than from the conflict as a whole.

Principle of Precautions

In the conduct of military operations, constant care must be taken to spare the civillian population (civilians and civilian objects).

Those who plan/ decide upon an attack should take all feasible precautions in the choice of means and methods of attack, with a view to avoid minimising incidental loss of civilian life, injury to civilians, and damage to civilian objects.

Feasible Precautions:

This refers to measures taken which are practicable, taking into acount all circumstances at the time.

Additional Protocol I provides that precautionary measures must be taken by both the attacking party and the attacked party.

• Attacking party:

Before an attack, those who plan or decide upon the attack must do everything feasible to verify that thier targets are military and not civilian in nature. They must assess excessive collateral damage and refrain from attacking if this paramter is reached.

The attacking party must give effective advanced warning (via digital means/ leaflets dropped from aircraft).

During an attack, the attacking party is obliged to cancel or suspend the attack if the target was at first mistakenly identified as being military in nature, or if the collateral damage appears to be more significant than anticipated.

• Attacked party:

The attacked party must remove the civilian population under their control from the vicinity of military objectives if at all possible. They must avoid locating military objectives near populated areas and must take all other precautions necessary e.g. creating shelter, distributing information about expected attacks, and evacuation procedures.

The principles of proportionality and precautions further restrict the ways in which hostilities can be conducted by parties to a conflict. In order to minimise the effects of war, the warring parties must ensure that an attack does not cause excessive collateral damage. Attacks should be planned carefully, civilians should be well informed, and relevant precautionary measures should be taken to protect civilians and civilian objects during armed conflict.