A committee ceases to do useful work when it passes 20 members.
At least, that is the theory put forward by distinguished British historian C Northcote Parkinson in a semi-serious essay on government.
It is not hard to imagine what he would have made of the European Commission, on which 28 nations are represented.
Critics say its size makes it unworkable.
The original six members may have been able to act in unison, but the point at which efficient discussion and decision-making was possible has long since passed, they say.
Yet the EU is determined to grow.
The more nations, the larger the internal market for goods and services; economic output can be scaled up to better compete with the US and China.
On an individual level, everyone benefits: citizens enjoy greater freedom to live, work and shop. This raises a number of questions that crop up in elections across Europe.
Should the EU become larger than it is at present? Is there an optimal “Goldilocks” size or could it expand indefinitely? We could also ask whether the EU is already too big.
Claude Miqueu, a former French Socialist MP, says the bloc needs to shrink to about 10 really committed countries with truly common objectives, so as better to face “threats from globalised capitalism”.
“If we persist with the Europe of 27 or 28 [with Britain], we supply the conditions for far-right parties to prosper,” he said. Such an extreme view is rarely heard, however.
If Brexit has proved one thing, it is how hard it is for a country to withdraw.
Chances are the EU will be adding, not subtracting. It welcomes approaches from new countries that “respect [its] democratic values” but is demanding in its criteria.
A country is intensively screened before it embarks on candidature, negotiation and finally accession. It all takes time, because it may be required to do more to reach the standards.
Not every country in the continent of Europe wants to join and not all are eligible. Some consider the pros and cons and decide not to.
In 2015, Iceland dropped its plans to join. Norway prefers not to fully join the EU, though, as a member of the European Economic Area, it abides by free movement, pays large sums to the EU budget, and follows many EU rules in order to participate in the single market.
Switzerland is also content to stay out, but has a very close relationship with the EU due to a network of bilateral treaties.
Small countries generally want to join because of access to markets and a greater voice.
Success has to be measured over the long term. Membership took underdeveloped, post-Franco Spain, for instance, and turned it into a modern country.
Ireland went from dispatching emigrant workers to receiving immigrants for its high-tech industries in a short space of time – and its views were backed to the hilt by other EU nations in the Withdrawal Agreement negotiations with the UK.
Membership is also desirable for eastern and central European nations, and arguably the accession of many of them in 2003 and 2007 benefited by helping them develop into peaceful democracies after the Iron Curtain came down.
Negotiations are under way with Montenegro and Serbia, and were waiting to start with Albania and North Macedonia. Bosnia-Herzegovina and Kosovo are “potential candidates” for future consideration. The last country to join the EU was Croatia, on July 1, 2013.
Turkey is also, nominally, in talks.
That sent shockwaves during the Brexit referendum campaign. Is it a democracy? Isn’t it culturally different? Would it dispatch hordes of migrant workers? Besides, 97% of it is in Asia. It should be noted, however, that when the EU expanded in the early 2000s, existing members were allowed to implement seven years of restrictions on the right to come to work, which the UK opted not to do.
Furthermore, the UK had a veto, but was one of the states most in favour of Turkey joining the union.
In fact, talks with the country have stalled since 2016, with the EU criticising its government over human rights. Out of 35 areas where it needs to comply with EU laws to join, only one has been signed off.
Simon Usherwood, deputy director of The UK in a Changing Europe thinktank, said the EU is adaptable and “could certainly cope with the handful of countries engaged in the joining process”.
However, Russia would be a different matter, he said. “That would be a very large new member which would have very substantial difficulties being incorporated.”
Any new member is likely to contribute turbulence as its economy aligns with the existing members. Excessive migration and “social dumping” can cause tension. But it will also bring benefits, such as increased cultural and linguistic variety.
Populist Eurosceptics insist that such variety is another source of tension and the union will not be able to hold itself together.
Some country will go the way Greece almost did and default, or else another will vote to leave. It is notable, however, that the “copy-cat” effect some predicted after Brexit has not materialised
New European Commission president Ursula von der Leyen said: “As paradoxical as it sounds, the shock of Brexit has strengthened our unity because it has not only shown what it means to leave, but also how much each country stands to gain as part of the European Union.”
More members also undermines the theory of a superstate in the making: the greater the diversity, the harder it will be for a cabal in Brussels to synchronise their political systems under one direction.
Another possibility is that we could see the emergence of a two-speed Europe, in which a core has the full experience while a peripheral band prefer Europe à la carte.
But, as Mr Usherwood puts it: “Why would you want to be a second-class member?” Despite populist disgruntlement, full EU membership is still seen as a desirable future for countries that can afford the fees and are willing to abide by the strict rules.