The Introduction defines the aims of the book and raises the problems it will deal with. The first aim is that of the philosopher of linguistics, namely, to reveal basic characteristics of linguistic theory formation that have been unknown so far and would thus clarify important foundational issues. Second, the book also aims to show how our metatheoretical analyses will provide findings that are capable of substantially improving the practice of problem solving in theoretical linguistics. This aim is that of the linguist – however, supported and furthered by the metatheoretical findings of the philosopher of linguistics. In order to reach both aims, the book tackles the problem of how inconsistencies emerge in linguistic theorising, under what conditions they can be tolerated, and how they can be resolved. Since this Main Problem is very complex, we divide it into eight more easily accessible sub-problems, whose solution will in the long run lead, step by step, to the solution of our Main Problem.