Famously, the Dominican friar used it to define the conditions for a “just war” and, while these provide a handy tick list to excuse military action, they can also be applied to political actions which have the potential of causing massive disruption. In this sense his theory is at the heart of the strategy of the SNP’s 56 MPs as they search for a reason to hold a second independence referendum.
The SNP know that to have a referendum they need, as Aquinas puts it, “legitimate authority”, but to have this they also need to find what he describes as “a just cause”. This is why, having suffered one defeat almost a year ago, the newly elected SNP MPs are preoccupied with the question of explaining why – despite Alex Salmond and Nicola Sturgeon’s promise – the referendum was not “a once in a generation” event.
Already a still pained Mr Salmond, who seems intent on blaming defeat on alleged broken promises by the pro-UK parties and the BBC rather than failings with the Yes arguments, has identified several possibilities – continued austerity, a failure to meet “the Vow” on more devolution, or the possibility of the UK voting to leave the European Union and Scotland voting to stay in. The problem with these points are that the Vow is arguably being delivered with a significant amount of devolution on tax and welfare; austerity was ongoing when Scots voted last year, and the EU referendum date has not even been set yet.
But, with George Osborne’s visit to Faslane yesterday, another issue raised its head and is becoming an increasingly likely “just cause” for the SNP – the replacement of Trident and plans to maintain the nuclear deterrent for another five decades on the Clyde.
The SNP always point out that civic Scotland opposes Trident, Holyrood has voted against it and 57 of the 59 Scottish MPs (the SNP 56 plus Labour’s Ian Murray) oppose its replacement.
The Tories, though, are set to press ahead and will have a final “gateway decision” vote in a matter of months. The SNP will argue then that nuclear weapons are being imposed on Scotland against its will and this could be the reason given in the Holyrood election manifesto for a second referendum on independence. If they are, as some SNP MPs are claiming, to have a referendum before 2020 then Trident is the best bet to legitimise it.
However, what might hold them back is another condition identified by Aquinas, “the probability of success”. Ms Sturgeon and her supporters know a second failure would end the debate.