The rise of the European Union (EU) provides an important case where the causal impact of ideas is unusually easy to demonstrate for several reasons. The EU project very explicitly featured what were perceived as new ideas. It altered major institutions in a relatively short period of time. It also centered on a relatively small number of political elites. Most importantly, elite patterns of support for the EU project turns up fortuitously clear foundations for an argument about the autonomy of ideas. Political debates over supranationality have cross-cut the main organizing lines of European politics to a striking degree. This pattern undercuts attempts to explain the EU project as any sort of straightforward, rational responses to salient patterns of an objective environment. Whether we consider how Europeans were collectively positioned in states, classes, parties, bureaucracies, sectors, or regions, we find that people in the same positions tended to disagree as much as they agreed about how supranational institution-building would harm or benefit them. They have fought a battle of ideas that their objective "interests"-by which non-ideational scholars really mean their position in some sort of unambiguous obstacle course-were unable to decide for them.The unusual clarity of the role of ideas in EU history points to opportunities for ideational scholarship more broadly. It highlights how attention to fairly concrete positional patterns of political action (or the lack thereof) can complement more common ideational methods of process tracing and interpretation, even in situations without such dramatically cross-cutting constellations. It also showcases rather starkly some problems with non-ideational scholarship that extend well beyond EU studies. In a case where divided elites perennially shouted at each other about explicitly new ideas, non-ideational social scientists did their best to boil the politics down to straightforward reactions to positions in an evolving obstacle course. They managed to hold to such accounts by relying mainly on fairly narrow and selective process tracing of events rather than systematic research on the positional patterns implied by their theories, and by filling in the resultant gaps in their accounts with post hoc functionalism. I suggest that these errors were made possible by a pursuit of non-ideational hypotheses without serious consideration of ideational alternatives. In EU history, like in many other settings, non-ideational theorists have held a debate only between positional arguments. They asked only what kind of positional pattern lay behind political outcomes, seeing little reason to look for debates or mobilization that cross-cut material and organizational positioning. Ideational explanation, by contrast, is built on the notion that action can vary independently from objective positioning. Its logic instructs us to investigate closely the relationship between positioning, ideas, and action, since there may well be multiple viable ways to interpret any position. This is certainly not to say that ideas always strongly cross-cut objective positioning. But this case where they did displays dramatically why non-ideational theorists too must entertain the possibility of idea-caused variation to test their own claims seriously. Moreover, it suggests that if traditional theorists overlooked the role of ideas here, where it is unusually easy to see, they have probably missed ideational causes in many other places as well. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]