Despite increasing attention to bilingualism--conferences, publications, grants--linguists are as far as ever from reaching consensus. Is code-switching the alternation between two equally activated languages or is it the insertion of elements from a source language into a recipient language? Can and should we distinguish borrowing and code-switching of single words? Is there grammatical convergence between bilinguals' two languages and does code-switching promote it? Since the first accounts of the structure of code-switching in the 1970s, the same questions have been readdressed with astoundingly little, if any, cumulative advances. Scientific progress has been obstructed by polemic debate, often fueled by elicited judgments, which may display random error (Labov, 1996), or reports of the behavior of stray individuals, which are uninterpretable in the absence of knowledge of the systematic community pattern (Labov, 2006/1966, p. 5).