My paper on the political philosophy of secession is now out in Public Affairs Quarterly, an open-access journal. Read it here. Teaser:
The United Kingdom currently sets the gold standard for management of secessionist politics. The British and Scottish governments negotiated in good faith over the terms of the independence referendum that Scotland held on September 18, 2014. If Scotland had voted to secede, the British government would have recognized its independence, thus affirming that the United Kingdom is a free partnership among its peoples.
Spain presents a different scenario altogether. Catalonia intends to hold its own “consultation” on independence, but the Spanish government has denied its right to do so, thus denying that Spain is a free partnership. The Catalan government has repeatedly sought to hold negotiations on the self-determination process, but has been rebuffed. What ought the Catalan government to do? By the criteria set forth in this paper, Catalonia has tried to conform to a just institutional regime for regulating secessionist politics, while Spain has not. Catalonia would be justified in using all proportionate means to secure a just outcome.
PILEUS 
Define “all proportionate means” please?
Means that cause less harm than the harm they remedy. Threatening Madrid with a dirty bomb=clearly disproportionate. Prohibiting taxpayers from sending tax payments to Madrid and requiring them instead to send them to a new tax agency in Barcelona=definitely proportionate.