Syntactic complexity has always been a matter of intense investigation in formal linguistics. Since complex syntax is clearly evidenced by sentential embedding and since embedding of one clause/phrase in another is taken to signal recursivity of the grammar, the capacity of computing syntactic complexity is of central interest to the recent hypothesis that syntactic recursion is the defining property of natural language. In the light of more recent claims according to which complex syntax is not a universal property of all living languages, the issue of how to detect and define syntactic complexity has been revived with a combination of classical and new arguments. This volume contains contributions about the formal complexity of natural language, about specific issues of clausal embedding, and about syntactic complexity in terms of grammar-external interfaces in the domain of language acquisition.

Until recently, little attention has been paid within syntax to components of discourse meaning that go beyond information structure and fall into the domain of non-at-issue meaning operating at the level of illocutionary force. To approach this domain, many of the contributions of this volume deal with the syntax of discourse particles. However, the issue of how to account for discourse particles within a more explicit map of the illocutionary domain is a good starting point for considering further phenomena related to the syntax of speech acts. By focusing on speech-act related particles and/or meaning domains, this volume makes a new contribution to the field, as existing collections either do not offer a comparatively narrow focus on particles or are not limited to syntax-oriented approaches. The primary audience of this volume are researchers and graduate students interested in state-of-the-art approaches to the syntax-discourse interface within the cartographic approach to syntax.

This special issue takes up three major concerns that have been raised by the recursion-only hypothesis by Hauser et al. (2002). The first concern is how to test for recursion in experimental psychology: Since we cannot test humans on infinite sets of sentences and furthermore self-embedding in the sense of (1) is difficult for humans to process, how can recursion best be tested for? The second major concern is the role of recursion in linguistic theory: Is recursion an integral part of any syntactic structure building or is recursion better viewed as something on top of more basic structure building? Finally, the third major concern this issue addresses is the relation of recursion to the genetic and neural basis of language. Can recursion be separated from other parts of language in the genetic and neural domain?