Europeans haven't agonized this much about Turkey since the Ottoman Empire was unravelling 100 years ago.
The geopolitics may have been very different in the age of kaisers and sultans, of imperial gambits and gunboat diplomacy. But one central question has persisted: What sort of alliance should bind Europe to the very different civilization on its eastern doorstep?
It's a question that is perplexing European Union leaders as they reach a critical juncture in deciding whether to throw open their doors to Turkish membership. Formal negotiations were scheduled to start Monday. But so fierce is the row that there were serious doubts at press time Sunday that the talks would start - with Britain urging members not to "abandon" Turkey even as Austria proposed a watered-down membership.
That is because EU enlargement is always controversial - and Turkey is proving the most controversial of the lot because of its striking difference from the European norm in terms of economics, demography, culture, religion, and even basic geography.
The crucial question is whether these differences will enhance or undermine the EU. Proponents say incorporating a Muslim-majority country for the first time will help the EU reach out to the Islamic world, and see Turkey's young, growing population and economy as a boon.
"A populous Turkey anchored in Europe would be a very good model and a great symbol to the Middle East, to the Caucasus, and to the Central Asian countries and others," says Fadi Hakura, a specialist at the London-based Chatham House think tank. "It's become the symbol of the merging of European and Western culture and Islam," he says.
This idea appeals to the Americans as well, and they have thrown their weight firmly behind Turkish accession, mindful that it will provide a bridgehead to the Islamic world and extend the EU's border up to Iraq and Iran in the east.
But opponents fret that a new member as large and poor as Turkey would adulterate European values. Lingering concern persists about the incorporation of 10 mostly East European countries last year, which some feared would dilute EU prosperity. Many feel that EU enlargement has run its course and that further extensions would make it unwieldy.
"Vienna must not become Istanbul!" has been the rallying cry in Austria, a notable antagonist, which up until the last minute was holding out for offering Turkey the lesser "partnership" deal instead.
Such opinions have been gaining currency this year. Two-thirds of Europeans oppose Turkish membership, according to a recent EU survey.
When French and Dutch voters abruptly rejected a new EU constitution in the summer, the Turkey question played a big role.
Since then, several EU heavyweights, from French would-be president Nicolas Sarkozy to German would-be chancellor Angela Merkel, have voiced grave doubts about Turkish accession.
An additional problem has been a lingering dispute over Cyprus, which Turkey refuses to recognize, but which is now an EU member.
EU members were also concerned by a recent attempt in Turkey to shut down a conference on the 1915 mass killings of Armenians, as well as moves to prosecute prominent author Orhan Pamuk over his use of the term "genocide" to describe the killings in a foreign newspaper interview.
Turkey itself has been upset by listening to Europeans discuss its merits and demerits in public. It is incensed that the Oct. 3 fanfare start date, formalized earlier this year, should now be called into question.
The foreign minister, Abdullah Gul, has warned that it may walk away from the process if fair play is not upheld.
That would be disastrous, say Turkophiles, warning of the terrible message it would send to the Islamic world.
Denis Macshane, a British MP and former Europe minister in the British government which as the current EU president is spearheading the talks, said that if the EU broke its word of honor it would "encourage nationalists and those who don't want Turkey to live by European norms."
He adds that for all Turkey's current problems with human rights, economic vacillation and security, the long process of getting it ready for EU membership will encourage it to raise its game - as it did with other EU newcomers.
"For the first time since Ataturk you have a real momentum for modernization, democratization, and economic reform in Turkey," says Macshane. "Istanbul is one of the cradles of European cultures and civilization. Turkey itself has got one foot in Europe and one foot in Asia. The question is do we want it to live under European norms and laws or tell it go off and imitate the worst performances of its neighbors?"