1. Key Principles: A few preliminaries
The Cardinal principles of IHL only applies under certain limited circumstances:
“armed conflict” threshold
Temporal scope of applicability (When?)
Spatial scope of applicability (Where?)
Why approach IHL through its cardinal principles?
Customary IL, some cases even peremptory norms, often codified or incorporated into treaties
Applies in all military operations when precise classification is uncertain
It doesn’t get any better, these often vague principles is often the only thing we have to rely on. For instance in targeting
A way of understanding more detailed IHL rules, often used when introducing IHL rules in combat training for example

2. IHL and the balancing of military necessity and humanity
Balancing of military necessity and humanity – the metaprinciple of IHL. ”embedded in every rule of the LOAC, one finds a balance between the principles of necessity and humanity.”
Balance (supposed to be) struck through the principles and the provisions of IHL not in the application phase (if this is not provided specifically at the level of the IHL norm).

3. Overarching Principles: Military Necessity
The principle of military necessity is in itself both allowing and restraining.
”Military necessity … has been defined as that principle which justifies those measures not forbidden by international law which are indispensable for securing the complete submission of the enemy as soon as possible.” (US Army Field Manual)
Is the authorizing element in IHL provisions restraining military force on the basis of considerations of humanity.
Explicitly invoked in IHL provisions offering room for deviation from a rule grounded in humanitarianism (see above).
Works in the background of the principle of distinction ex. AP 1 articles 51 and 52 implicitly offering space for deviation.
Works in the background of the principle of unnecessary suffering, implicitly recognising the lawful nature of weapons that cause “militarily necessary” suffering.

4. Overarching Principles: Humanity
Martens Clause, assertion that all military operations require considerations of humanity, even those that fell outside of the scope of treaties entered into by states. (Preamble 1899 Hague Convention, AP 1, art. 1(2)).
Humanity, essential counterbalance to the principle of military necessity and serves as an overarching principle of constraint in armed conflict.
Not an operative principle in the same way as, for instance, the principle of proportionality. Instead finds it’s expression in a range of IHL norms in counterbalance with ”military necessity”
”Humanity” is not a trump card . You may never deviate from an IHL obligation by reference to ”humanity”, same as with “military necessity”.

5. Implementation Principles: Distinction
ICRC Customary IHL study Rule 1. ”The parties to the conflict must at all times distinguish between civilians and combatants. Attacks may only be directed against combatants. Attacks must not be directed against civilians.”
ICRC Customary IHL study Rule 7. ”The parties to the conflict must at all times distinguish between civilian objects and military objectives. Attacks may only be directed against military objectives. Attacks must not be directed against civilian objects.
AP 1. art. 48. ”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 between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.” – AP 1 art. 52(2) “military objective”
Distinction: A means to limit war by directing it against legitimate targets. Works both offensively and defensively
An attack that fails in upholding distinction will be considered an indiscriminate attack.

6. Implementation principles: Proportionality
ICRC Customary Law Study Rule 14: ”Launching an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated, is prohibited.” (almost identical treaty provision found in AP I, article 51(b)).
Strives to reduce collateral damage in attack
Requires attacker to take precautionary measures such as to issue advance warnings etc.
What proportionality is not:
Only rules out excessive civilian casualties, does not men that they cannot be extensive.
Remember, different from proportionality in the jus ad bellum.
Also different from proportionality in human rights law.

7. Implementation principles: Unnecessary suffering
Rule 70: The use of means and methods of warfare which are of a nature to cause superfluous injury or unnecessary suffering is prohibited, Hague Convention art.
Offers restraint on the suffering inflicted on opposing combatants. Has been used to:
Ban weapons which increase suffering without increasing military advantage.
Together with distinction, most basic consideration in weapons legal review AP 1 art. 36

8. Spot the principle in IHL
1907 Hague Regulations article 23(second to last section)
GC AP1 art. 57 para. 1-3
GC AP1 art. 51 para. 7.
1868 St Petersburg Declaration on Explosive Projectiles sections 1 to 6.
GC AP1, art. 40
GC AP1, art. 58
Rome Statute art. 8(2)(b)(xiii)
GC AP1, art. 35 para. 1.
GC AP1, art. 58(b)

9. Human Rights Watch Q & A: 2014 Hostilities between Israel and Hamas
What guidance does the report give in relation to
Hamas and
Israeli
conduct as concerns
Distinction?
Proportionality?
Military necessity?
Humanity?
Unnecessary suffering?
What does the report say about:
What type of conflict? (IAC or NIAC?)
The application of the laws of belligerent occupation?
Jus ad bellum? Including customary restrictions on the use of force?
IHRL?

10. For distribution...
”Here’s what ”proportionality” in War Really Means” Time Magazine