Because the increasing heterogeneity of the member states will make it increasingly difficult to jointly develop policy, it is very sensible to allow flexible forms of integration. Fischer's ideas aim at a Europe of the avant-garde, that is, at a fixed group of countries that would work together and strive for deeper integration. One disadvantage of this idea is that it creates a two-class federation. This is also the reason that the candidates for entry into the EU have rejected the idea. Accordingly, Janos Martonyi, the Hungarian Secretary of State, characterised the concept as the "death-blow to integration." Hubert Védrine had already drawn attention to other problems: How would the members of Europe's avant-garde be selected? What would remain of Europe's avant-garde if, as Fischer desires, access to it were forced to remain open and all the member states wanting to belong to it?
A less politically explosive solution would allow the flexible and functional co-operation of various territorial units. Each group of member states from a particular governance area could join together to work on a given policy or task. The scope of the co-operatives would be adapted to the problems that were to be solved (e.g. the Alp states could work together to solve tourist problems or the states adjoining the Rhine could work on water-quality problems) or on the basis of political will (as with the common currency). Such co-operation ought to be possible for sub-national units as well, like the German Bundesländer or municipal bodies. The American special districts could serve as a model here: these are associations of municipal bodies that aim to solve particular tasks; they normally have tax sovereignty, and their top officials are often directly elected. The organisation of such member state or cross-border co-operatives of sub-national bodies would have to be regulated through the European Treaties. They could take the possibilities for "closer co-operation" established by in the Treaty of Amsterdam as their basis. Expanding "closer co-operation" to the sub-national units and easing the conditions required for it (eradicating the requirement for a minimal number of members and veto rights for individual member states) could make flexible and differentiated forms of integration of this sort possible.