Over the last week the world has been rocked by the unexpected—and, to many, inexplicable—vote of the British to leave the European Union. It’s a highly controversial move and one that many Americans do not have ready-made categories for understanding. Can Catholic social thought help us to sort through the debate?

I believe it can. In particular, two principles of Catholic social thought seem especially relevant: subsidiarity and solidarity.

Solidarity refers to the need to preserve and promote the common good. The principle of subsidiarity holds that a larger organization should not take on tasks or functions that can be handled by smaller, or subordinate, organizations.

On the surface, it may seem these two principles are in tension with each other. Solidarity seems to stress unity while subsidiarity tends in the opposite direction. But they really aren’t. One could think of the distinction in terms of ends and means. Solidarity is about ‘what’ we’re trying to achieve—subsidiarity concerns the ‘how’ of doing that.

The ‘common good’—that’s something we hear often. What does that really mean? A working definition might be those conditions conducive to human flourishing, to paraphrase Catholic Answers Magazine (which has a good synopsis and explanation of all the principles of Catholic social thought here). The common good means the good that is shared by all, rather than being simply the sum of what is good for each individual person, as Catholic Answers notes.

Fundamental to the Brexit debate is the question of exactly one draws the boundaries of what is deemed to be held in ‘common.’ By withdrawing from the European Union, has the United Kingdom, by definition, undermined the ‘common good’?

It’s here that the principle of subsidiarity might be of particular assistance. By many measures, the EU behaved like a state: it had its own currency, its own parliament, and even its own ‘taxes’ referred somewhat euphemistically as ‘dues’ since these were paid by member governments and not directly levied on citizens. This might seem like a usurpation of local state sovereignty, which is surely one of the arguments for exiting the union. Proponents of remaining within the union however would point to many benefits of membership: such as free trade and the free movement of people seeking jobs.

So far, Catholic social thought isn’t giving us definitive answers. But at least it helps us to ask the right questions. That, itself, is helpful to anyone wishing to dive deeper into the debate. (A good next step would be to review primers on Brexit, such as this one available from the BBC.)

One more principle of Catholic social thought might also come into play here—what is known as ‘the preferential option for the poor’ (A good definition is available here under the fourth item.) In the days since the Brexit vote, the apparent consensus of many is that membership in the European Union is, from an economic perspective, a good thing. But the Brexit vote certainly raises the question as to whether all sectors of British society, especially lower-income citizens, were sharing in those benefits. If so, the EU fails one of the basic tests of Catholic social thought, at least from the perspective of a British voter.

We usually think of Catholic social thought in terms of principles that inform the good and just ordering of a society. But the whole Brexit debate is as much a matter of domestic policy as foreign policy. So it’s also worth considering what the tradition of the Church might say when speaking from this perspective. This body of teachings is known as just war theory. Now no one is about to go war over Brexit, but it’s worth noting that one the EU has its roots in the post-World War II period. Creating a zone of free trade and the free movement of peoples, so the theory went, could reduce the chances of another war breaking out.

Also worth a brief mention is the Pastoral Constitution on the Church in the Modern World, also known as Gaudium et Spes, which was promulgated by the Second Vatican Council. Near its end, the constitution does endorse the notion of international cooperation and even international organizations, but this is primarily in the context of international aid and development—big issues in the 1960s. Also, Gaudium et Spes warns against any heavy-handed forms of internationalism that lack equity or compromise the freedom and independence of those nations they are supposedly benefitting.

That sort of cautionary note is reflected in Pope Francis’ own brief comments about Brexit when asked about it by the Register’s own Edward Pentin. Francis seemed to view the EU as an example of international “fraternity.” Then again, he also expressed support for another type of union with “more independence” and “more liberty” for its members.

The Brexit debate is a complex one. In this area, Catholic social thought does not have clear-cut answers. But it does shed some light one what otherwise might seem to many of us to be a murky issue.