1. The principle of distinction is the “foundation on which the codification of the laws and customs of war rests”.^[191] First set forth in the 1868 St. Petersburg Declaration,^[192] then reaffirmed in Art. 48 of AP/I,^[193] the principle is intended to protect against direct attack: (a) civilians unless and for such time as they directly participate in hostilities (see Section F); (b) civilian objects as distinct from military objectives (see Rule 1 (y) and Section E). The principle of distinction also underpins such obligations as the prohibition of indiscriminate attack (see Rule 13), compliance with the principle of proportionality (see Rule 14) and the requirement to take feasible precautions in attack (see Section G).
2. In its Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, the ICJ has recognized the distinction as one of the two “cardinal” principles of international humanitarian law, the other being the prohibition of unnecessary suffering.^[194] The ICJ, in that Advisory Opinion, stated: “States must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets.”^[195] The principle of distinction is indisputably a principle of customary international law.
3. Rule 10 (a), by confining attacks to lawful targets, rules out direct or indiscriminate attacks against civilians (unless and for such time as they are directly participating in hostilities, see Section F). Nevertheless, in warfare, civilians and civilian objects are often harmed, despite not being the object of direct or indiscriminate attack. This is principally related to collateral damage, governed by the principle of proportionality (see Rule 14).
4. An attack is unlawful if aimed at other than a lawful target (see Rule 10 (b)), even if it ultimately fails to cause actual harm.
5. Rule 10 (a) applies also in non-international armed conflict.

191. Para. 1863 of the ICRC Commentary on AP/I, pertaining to the Commentary on Art. 48 of AP/I.
192. Second paragraph of the Preamble to the 1868 St. Petersburg Declaration: “That the only legitimate object which States should endeavour to accomplish during war is to weaken the military forces of the enemy.”
193. Art. 48 of AP/I: “In order to ensure respect for and protection of the civilian population and civilian objects, the Parties to the conflict shall at all times distinguish be¬tween the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.”
194. ICJ, Nuclear Weapons Advisory Opinion, at Para. 78.
195. Ibid.

This Rule applies also in non-international armed conflict, although the term “combatant” is reserved for international armed conflict. Thus, like members of the regular armed forces of the State concerned, members of a non-State organized armed group in a non-international armed conflict are lawful targets.^[196]

196. According to the ICRC’s Interpretative Guidance on the notion of direct participation in hostilities, organized armed groups in a non-international armed conflict consist only of individuals whose continuous function it is to take a direct part in hostilities (“continuous combat function”).

1. The customary definition of combatants, originating in Art. 1 of the 1907 Hague Regulations,^[197] is found in Art. 4 (A) (1) and in Art. 4 (A) (2) of GC/III.^[198]
2. Combatants include all members of the armed forces of a Belligerent Party, except medical or religious personnel. The armed forces include the officially organized military forces, as well as organized armed forces, groups and units under a command responsible to a Party to the conflict and responsible for his subordinates; which wear a distinctive sign (e.g., clothing or other accoutrements) that distinguish them from the civilian population; carry their weapons openly; and which generally conduct their operations in accordance with the laws and customs of warfare.
3. Paramilitary or other armed law-enforcement agencies may be incorporated into the armed forces. When this occurs, the members of such agencies become combatants. In other words, incorporation renders them lawful targets. Art. 43 (3) of AP/I requires such incorporation to be notified to the other Belligerent Party.^[199] However, failure to so notify the enemy does not bar their treatment as lawful targets.
4. Disagreement exists as to whether individuals who do not meet the aforementioned criteria, but nevertheless participate directly in the hostilities, are to be characterized as “civilians” or “unprivileged belligerents” (also termed “unlawful combatants”) (see paragraph 4 of the Commentary on the chapeau to Rule 111 (b). The issue whether they are “unprivileged belligerents” is relevant only to the rules governing their detention (as POW, civilian internees or under some other category). However, it is clear that civilians who participate directly in hostilities can be attacked or captured no matter whether they are characterized as “civilians” or as “unprivileged belligerents” (see Section F).
5. Persons, including combatants, who are hors de combat may not be attacked (see Rule 15 (b)).
6. Certain categories of individuals are singled out in the law of international armed conflict as enjoying specific protection because of the functions they serve. Apart from medical and religious personnel (see Section K), this refers to civil defence personnel which may not be attacked unless they commit acts harmful to the enemy (see Section N (I)). It ought to be noted that civil defence functions can be performed by a military unit. The personnel will remain protected, provided that they are permanently assigned and exclusively devoted to the performance of civil defence tasks (see Art. 67 of AP/I).^[200] The performance of recognized civil defence functions is in this connection not considered harmful to the enemy, even when amounting to putting out a fire on a military objective, if the fire endangers the life of civilian persons or threatens civilian objects in the vicinity (see paragraph 3 of the Commentary on Rule 1 (k)).

197. Art. 1 of the 1907 Hague Regulations: “The laws, rights, and duties of war apply not only to armies, but also to militia and volunteer corps fulfilling the following conditions: (1) To be commanded by a person responsible for his subordinates; (2) To have a fixed distinctive emblem recognizable at a distance; (3) To carry arms openly; and (4) To conduct their operations in accordance with the laws and customs of war. In countries where militia or volunteer corps constitute the army, or form part of it, they are included under the denomination ‘army’.”
198. Art. 4 of GC/III: “(1) Members of the armed forces of a Party to the conflict as well as members of militias or volunteer corps forming part of such armed forces. (2) Members of other militias and members of other volunteer corps, including those of organized resistance movements, belonging to a Party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that such militias or volunteer corps, including such organized resistance movements, fulfil the following conditions: (a) that of being commanded by a person responsible for his subordinates; (b) that of having a fixed distinctive sign recognizable at a distance; (c) that of carrying arms openly; (d) that of conducting their operations in accordance with the laws and customs of war.”
199. Art. 43 (3) of AP/I: “Whenever a Party to a conflict incorporates a paramilitary or armed law enforcement agency into its armed forces it shall so notify the other Parties to the conflict.”
200. Art. 67 of AP/I, see fn. 513.

1. Military objectives, as defined in Rule 1 (y), are classified by nature, location, purpose or use. The criteria of use, location or purpose may turn an otherwise civilian object into a military objective in certain circumstances (see Rule 22).
2. Under Art. 59 (2) of AP/I, a Belligerent Party may declare any inhabited place in or near the contact zone as a non-defended locality (subject to several conditions, such as that all combatants, mobile weapons and mobile military equipment must have been evacuated, that no hostile use will be made of fixed military installations or establishments located therein).^[201] The concept goes back to Art. 25 of both the 1899^[202] and the 1907^[203] Hague Regulations.^[204] A declared non-defended locality must not be attacked. However, the entire construct is based on the idea that it is situated in or near the contact zone, thereby allowing the enemy to enter the locality whenever it desires.

201. Art. 59 (2) of AP/I: “The appropriate authorities of a Party to the conflict may declare as a non-defended locality any inhabited place near or in a zone where armed forces are in contact which is open for occupation by an adverse Party. Such a locality shall fulfil the following conditions: (a) all combatants, as well as mobile weapons and mobile military equipment must have been evacuated; (b) no hostile use shall be made of fixed military installations or establishments; (c) no acts of hostility shall be committed by the authorities or by the population; and (d) no activities in support of military operations shall be undertaken.”
202. Art. 25 of the 1899 Hague Regulations: “The attack or bombardment of towns, villages, habitations or buildings which are not defended, is prohibited.”
203. Art. 25 of the 1907 Hague Regulations: “The attack or bombardment, by whatever means, of towns, villages, dwellings, or buildings which are undefended is prohibited.”
204. Art. 59 (1) of AP/I: “It is prohibited for the Parties to the conflict to attack, by any means whatsoever, non-defended localities.”

Civilians who directly participate in hostilities lose their immunity from attack for such time as they so participate (see Section F). Although they have no combatant rights, they may be directly attacked like combatants. Yet, once they become hors de combat they are subject to — and benefit from — the application of Rule 15 (b).