When Theresa May comes to the House of Commons on Monday afternoon, she will face two major questions about Saturday's bombardment of Syria: was it legal, and should she have sought prior authorisation from parliament? The government set out its answer to the first question in a document on Saturday, arguing that it is permitted under international law, on an exceptional basis, to take measures to alleviate overwhelming humanitarian suffering.
To use force on the basis of humanitarian intervention, it said, three conditions must be met. There is convincing evidence, generally accepted by the international community as a whole, of extreme humanitarian distress on a large scale, requiring immediate and urgent relief. It must be objectively clear that there is no practicable alternative to the use of force if lives are to be saved. And the proposed use of force must be necessary and proportionate to the aim of relief of humanitarian suffering and must be strictly limited in time and in scope to this aim (ie the minimum necessary to achieve that end and for no other purpose).
Monstrous suffering
The government says that Bashar al-Assad's record shows that he would use chemical weapons again if he could, adding to the monstrous suffering he has brought down on his own people during seven years of civil war. It argues that Russia's veto at the United Nations of western efforts to relieve humanitarian suffering in Syria meant there was no alternative to military action.
Jeremy Corbyn has questioned this legal argument, arguing that humanitarian intervention is a legally debatable concept. The Labour leader has also protested against May's failure to seek prior approval from parliament, as Tony Blair did before the Iraq war in 2003 and David Cameron did before he attacked Libya in 2011 and, unsuccessfully, two years later when he wanted to attack Syria.
May's allies insist that there is no need to consult parliament before a limited military operation such as Saturday's and some hawkish Conservatives are eager to put an end to the convention Blair introduced. Corbyn's view on parliamentary authorisation is shared, however, by the Scottish National Party, the Liberal Democrats and the Greens, as well as the overwhelming majority of Labour MPs, including many who believe the air strikes were justified.
It is also shared by a sizeable minority of Conservatives, including parliamentary heavyweights such as former chancellor Ken Clarke, who are likely to give the prime minister a tough grilling in the Commons on Monday.