No panacea: the carrot of EU accession has not yet persuaded Bosnia's leaders to set aside their differences. Photograph: European Commission

Presenting his annual progress report on the applicant countries in October, Commissioner Olli Rehn stated that “political de-mining” was part of the EU's job when it came to enlargement. He was referring to the countries of the western Balkans, with their persistent infighting. But he might as well have been talking about some of the EU's existing members.

With the Lisbon Treaty finally ratified, the enlargement debate may soon return to the top of the EU agenda. The “wideners” will be back to stress the importance of further expansion for Europe’s global aspirations. Opponents will reiterate warnings about the challenge enlargement poses to the European polity and its identity. Both lines of argument have strong justifications. Yet both tend to overlook a basic point: EU expansion has helped to foster prosperity, spread peace and consolidate democracy in the candidate countries and in Europe as a whole.

First and foremost, enlargement is a tool for achieving those goals, not the goal itself. And the EU is not ready to lay down that tool just yet. Brussels' credibility in the Balkans rests on its ability to fulfil the membership pledge as soon as the applicant countries have met the agreed conditions (though as Bosnia's enduring fragility shows, that pledge is not always sufficient to keep candidates on the reform track). The recent Turkish-Armenian accord may lend a new lease of life to Ankara’s EU bid, which should in turn remind EU governments that their contradictory position on Turkey cannot be maintained indefinitely. The domestic mayhem in countries such as Ukraine and Moldova means that their accession is not a topic for now - but the EU will, at some point, have to find a conclusive answer to these states' long-term membership aspirations.

Only when the EU resolves this principled ambiguity will it be able to focus on the instruments at its disposal. And when that happens, it will become clear that in many key areas, the path before Europe is largely laid out already. "Deep" free trade arrangements, such as that being negotiated with Ukraine, will open up the EU market and spur substantial economic integration with its neighbours. Some neighbours have provided significant assets in specific EU foreign policy missions - witness the Moroccan troops deployed in Bosnia. Visa liberalisation is the name of the game in the Balkans.

So in time, some of the EU's neighbours may be surprised to discover that the difference between member state and partner state is increasingly blurred. A candidate country like Turkey may have to swallow a restrictive EU accession deal, replete with exceptions and "safeguards". But for a country such as Israel, which is in many fields deeply integrated with the EU already, the question of membership has long been redundant.

No neighbourhood policy or "privileged partnership” will ever match the appeal of membership. Yet the only way for the EU to break free of the circular enlargement debate of the past half-decade is for it to focus on the concrete benefits that existing instruments can deliver, and to keep bickering to a minimum.