In the past few days, in the wake of ISIS's horrific burning of a Jordanian air force pilot, Jordan has adopted a highly combative tone toward the group. It has matched this rhetoric with action: Its air force carried out dozens of strikes against ISIS targets on Thursday. This is a significant increase from the number and pace of strikes that Jordan previously had undertaken as part of the coalition using force against ISIS in Syria. Jordanian Foreign Minister Nasser Judeh stated that these airstrikes mark the beginning of his country's retaliation for the pilot's death, and he vowed to destroy ISIS. In his words, "We are upping the ante. We're going after them wherever they are, with everything that we have. But it's not the beginning, and it's certainly not the end."
This clearly is an important shift politically, both for Jordan and for the anti-ISIS coalition, but does it mean anything legally? It's possible to construe Jordan's statements as indicating that Jordan is now acting in individual self-defense, rather than -- or in addition to -- the collective self-defense of Iraq. If Jordan believes that the burning of the pilot effectively constituted an armed attack on Jordan itself, an individual self-defense theory could flow from that. (Many might be concerned about interpreting that event as an armed attack, though states historically have proven willing to use force to defend their nationals abroad when they come under threat, treating their uses of force in that context as a subset of individual self-defense.)
If Jordan is simply layering an additional international legal theory (individual self-defense) onto its existing legal theory (collective self-defense of Iraq), that should have no implication for the military actions Jordan undertakes. If, however, it perceives some segment of its airstrikes as being conducted exclusively under its individual self-defense theory, that would affect its military actions because it would require a different proportionality calculation. That is, its strikes against ISIS in individual self-defense would need to be proportional to the attack that triggered that right: the immolation of the pilot. That would seem to require a much more constrained response than that permitted in the collective defense of Iraq.
It is certainly possible that Jordan's recent public statements are driven entirely by politics, and are not intended to signal a change in its legal approach to its airstrikes. Future Jordanian statements and actions may illustrate more clearly how we should interpret the comments of the past two days.