Since Chomsky's barriers, functional heads have been the prime target of research in the generating linguistics. But over the past two decades, two competing approaches have developed.

The mapping project, as mentioned in these Oxford series collections, is evidence of a functional head in one language as evidence in general rules. On the other hand, simplified calculations tend to look at the structural economy as literally having as few heads as possible.

In the current volume, some of the most influential linguists involved in this protracted debate present their latest work in short, self-contained case studies. Contributions cover all the major layers of the newly studied grammatical structure, including the main areas of experimental research such as grammatical and language change, standard and non-standard items, interface problems, and morphosyntax. Functionaries attempt to map the grammatical aspects following the mapping approach, thus showing that the differences between the mapping approach and the intuitive approach are more obvious than the substance..