This chapter introduces a number of key concepts that are important throughout the book. It offers an informal discussion of the nature of universality; an important, related, distinction between types of explanatory why-questions; and a distinction between kinds of potential reductive relations between theories. I provide a broad overview of the role asymptotic reasoning plays in the proper understanding of explanation, reduction, and emergence.
Keywords: asymptotic reasoning, emergence, explanation, reduction, regular limits, singular limits