Military objectives must by their nature, location, purpose or use make an effective contribution to military action AND the total destruction, capture or neutralization, in the circumstances, ruling at the time, must offer a definitive military advantage. 2 conditions
By nature, purpose or use make an effective contribution to military action
So, a civilian object may become a military objective only if it makes an EFFECTIVE contribution to military action.
Contribution must be effective: the contribution must be directed towards the actual war-fighting capabilities of the adversary and not merely war-sustaining capabilities
Definite military advantage. The advantage must be concrete, perceptible and the commander must have clear information about this advantage
Must be a MILITARY advantage (not political, economic, ...°
In the circumstances reling at the time: if an object does not yet or does not anymore provide military advantage -> no attack. NO PREEMPTIVE DESTRUCTION
Eg military airport, weapons storage site -> targetable