There has been an interesting and robust debate on Just Security over the past several weeks regarding the issue of the use of force on the territory of another state, but not directed against that state (here, here, here, and here).  The issue is whether the use of force on the territory of a state, but not directed against the territorial state, triggers an International Armed Conflict between the intervening state and the territorial state (for example, the United States and Syria).  This discussion is predicated on the fact that the territorial state has not consented to the use of force by the intervening state.  Ryan Goodman addressed the nature of consent in Syria nearly two years ago in a post on Just Security.  Given the current debate and the intervening two years, it is worth again considering the notion of consent, and, in particular, tacit consent.  

Under Article 20 of the Articles of State Responsibilityconsent is a circumstance precluding wrongfulness. Specifically, consent from the Syrian government to the United States and coalition forces would make their use of force in Syria lawful.  Consent would have the further effect of rendering moot the possibility that an International Armed Conflict is triggered when, for example, the United States attacks ISIS in Syria.  Plainly, the United States and coalition forces are not operating in Syria with the express consent of the Syrian government.  Indeed, Syrian officials have made statements to the contrary, and neither the U.S. nor any allied country has cited consent as the grounds for the use of force.  That said, Syria has never filed a formal protest with the Security Council nor taken any defensive actions against the United States, despite having a robust integrated air defense system.  Is it possible then that the U.S. and coalition forces are acting with the tacit consent of Syria? 

There are well-accepted limitations to the concept of consent.  According to the commentary to Draft Articles of State Responsibility, consent must be freely given by an agent with the authority of the state before the use of force, and it may be revoked at any time.  The Articles of State Responsibility (Article 20) are silent on the nature of the requisite consent.  The commentary to Draft Articles, however, notes that consent must be “valid” and “actually expressed by the State rather than merely presumed on the basis that the State would have consented if it had been asked.”  The consent need not take a particular form, nor must it be in writing.  The Articles do not require that the consent be explicit or expressly stated.  Special Rapporteur Roberto Ago found that consent can be “expressed or tacit, explicit or implicit provided, however, that it is clearly established.”  In his treatise on state responsibility, James Crawford also concludes that consent may be “tacit or implicit rather than communicated in some formal way.”  

The commentary to the Draft Articles points to the Savarkar case, where the Permanent Court of Arbitration found that France impliedly consented to a British breach of their sovereignty where French police forces assisted British personnel to make an arrest on French territory.  Similarly, in the Armed Activities case, the ICJ considered the Democratic Republic of the Congo’s objection to the presence of Ugandan troops in its territory. The court found that consent existed despite the lack of formal agreement requesting or consenting to the Ugandan troops.  There the court found consent in the lack of “objection to the presence of Ugandan troops.”  In short, valid consent can be express or implicit and need not take a particular form.  

So what do we make of the fact that Syria has never formally objected to the U.S. activities in its country?  Its lack of clear objection is particularly noteworthy given vocal Syrian opposition to other incursions in its territory.  As pointed out by Ryan Goodman in his earlier post on the topic, Syria has taken formal steps to object to use of force on its territory by Israel and Turkey and also formally objected to the delivery of humanitarian aid without its consent.  Syria has not formally objected to coalition military activity, and has not activated its sophisticated integrated air defense systems or otherwise sought to enforce its borders against U.S. and coalition activities.  Indeed, President Assad has acknowledged receiving intelligence reports regarding U.S. and coalition air strikes.  Further, President Assad has also publicly stated his support for an agreement, which by its terms does not apply to U.S. and coalition actions against ISIS or al-Nusra despite the fact that these international forces are engaged in daily airstrikes against both groups in Syria.  

These facts could all be construed to indicate tacit consent.  That said, Roberto Ago cautioned that “presumed consent should not be confused with tacit consent.”  While the United States and coalition forces are not acting in Syria with the express consent of the Syrian government, an argument for consent is grounded in something more than the speculative presumption of consent.  Here there are objective facts which could reasonably be seen as elements of tacit consent.  

If, arguendo, the Syrian government does not in fact consent to the use of force, how might it express this lack of consent?  More fundamentally, is there an obligation on the part of the territorial state to express their lack of consent to a use of force on their territory? There does not appear to be such an obligation in international law.  Indeed, the fact that consent cannot be presumed weighs against such an obligation:  if consent cannot be presumed, it surely follows that there is no requirement to express a lack of consent.  

Where, however, a state has acted in ways that render the lack of consent questionable, it seems advisable as a practical, if not legal, matter to make clear their lack of consent.  Similarly, while Syria’s expression of non-consent need not take a particular form, it would seem good practice to unequivocally articulate its position.  Assuming then that Syria wishes to express its lack of consent, it may most obviously do this through its actions such enforcing its borders.  Here one could argue that Syria has failed to do this not because it implicitly consents, but rather it fears the military response which would inevitably follow the shoot-down of a coalition plane.  While true, there are other methods to express Syria’s lack of consent.  A letter to the Security Council would be a clear manifestation of its intent—and a measure it has taken in the past.  Further, Syria could also manifest its lack of consent through an express statement by the president or foreign minister.  

The views expressed are the author’s own and do not represent the U.S. Department of Defense or any other government entity.

Image by Seaman Christopher A. Michaels, U.S. Defense Department