A few days ago ago I tweeted this line: “Secession is the decision to step out of an existing political order, so it’s a category error to try to justify it legally.”
Obviously I’m not going to solve all of the problems of a burgeoning sub-discipline of political philosophy with a single tweet. But it seems I’ve set off a big discussion anyway, so I’d better join in.
I generally agree with Drumm’s and Kuznicki’s condemnation of libertarian defenses of Confederate secession. But I don’t think that legal secession is necessarily a “category error.” Like many other legal relationships – partnerships, clubs, corporations – a federal system of government can incorporate rules that provide for its own dissolution. For example, the Canadian Supreme Court has ruled that Canada’s Constitution allows Quebec to secede so long as the secessionists prevail in a referendum and negotiate certain issues with the rest of Canada. If Quebec does secede in the aftermath of a secessionist referendum victory, the resulting secession will be perfectly legal under Canadian law. There are other federal constitutions that explicitly provide for a right of secession. The most famous recent example is Article 72 of the Soviet Constitution, which numerous constituent republics seceded under in 1990-91.
Of course, it’s indisputably true that some secessions are authorized by some countries’ constitutions. Others, however, are not. Within these two types of cases, authorized and unauthorized, we can also imagine specific acts of secession that we find ethically justified or ethically unjustified.
That a given constitution forbids secession does not in my view mean that all secessions from it are necessarily unjustified. It means only that we have to justify them through extraconstitutional means, and these means must in themselves be weighty enough to also justify overthrowing the existing legal order.
Similarly, that a given constitution allows secession does not in my view automatically justify all secessions carried out under it. We may still find some of them ill-advised or even unjustified. There’s nothing about constitutional law that says that where the law permits a thing, the conscience has to be silent.
That said, secession has a much lower bar to clear in cases where it is constitutionally authorized. In such cases, the secession doesn’t have to be for a weighty enough cause to justify the overthrow of the existing legal order. A secession for relatively indifferent things might be permissible. Indeed, if the constitutional requirements for secession are easy enough, we should expect them to occur fairly often and for trivial reasons.
Jason Kuznicki and Ilya Somin make the critical error of mistaking “secession” for “revolution.” Revolution means to overthrow a political and legal order, while secession is a legal theory—it is the theory that for a state to leave the union is itself within the legal order. It is therefore literally incorrect to say that secession is the “attempt to step outside the legal order.” That’s revolution. The American Revolution was not an attempt at secession—note that the word was virtually never used by the Revolutionary leaders. On the contrary, the term secession came into use in the decades before the Civil War as an attempt to justify a (pseudo-)revolutionary act within the legal order.
Not all revolutions, however, involve one government at the start and two or more at the end. The American Revolution was relatively unusual in this way. And secessions carried out according to a constitution that authorizes them are perhaps not always rightly considered revolutions, depending on what other changes are carried out along the way.
So ultimately, “the law says we can” or “the law says we can’t” doesn’t answer the question of whether a given secession is a justified act. To answer it, you may also have to appeal to something outside the law.
Aside from that, I agree with Sandefur that the U.S. Constitution does not permit secession. I think it’s very clear on that point right now, and indeed it was clear (although slightly less so) in 1860. The southern secession was thus constitutionally unjustified. It was also ethically unjustified, because its purpose was to protect the institution of slavery.
Indeed, if by an act of secession the North might have ended slavery, then it would have been justified in doing so, the 1860 Constitution notwithstanding, because ending slavery is in my judgment a weighty enough reason to overcome whatever respect one might have for an existing legal order.
 To use the term “secession” in a way that refers only to the American South or to other cases strictly of its type would rob us of any ability to do comparative work on phenomena that nonetheless manifestly deserve to be compared (or at times contrasted) to one another. Secession is not just a quirk of American law. And it is no insult to the American Revolution to call it a secession, even if the founders never used the term. Legal and ethical permissibility may vary arbitrarily across different acts of secession, just as it does with various business transactions or, indeed, with various types of killing.
 Yes, I know about Lysander Spooner and Frederick Douglass, and their arguments that the 1860 Constitution was already sufficient to abolish slavery. While I find them interesting, I am not taking these arguments to have any force for the purposes of our discussion.