Introduction

In this introductory chapter we present some central philosophical views and problems about the notion of levels of reality that will be further explored in the chapters of this volume. We point out that the question whether reality has a multi-level structure is a deep philosophical issue with widespread implications for how we think about central problems in philosophy and science. We emphasise the many aspects of the notion of levels, distinguish between ontological levels (where levels are used as a way to talk about the hierarchical structure of the world) and epistemological levels (where levels have primarily a methodological and epistemological role) and explore their complex relationship. We also discuss the general reasons offered by non-reductive physicalists to adopt a metaphysics of a multi-level reality and whether the levels described by such accounts of the special sciences can be part of a physicalist ontology.