Levels1 Introduction2 Refining the levels metaphor: Three defining questions3 From gesture to prototype4 Levels of sciences and theories5 Size levels 6 Parts and wholes6.1 Types and tokens of parts and wholes6.2 Mereology6.3 Levels of organization: Aggregates and mechanisms6.3.1 Levels of mechanisms are local6.3.2 Placement is weak and derivative in levels of mechanisms6.3.3 Emergence and levels of mechanisms 6.3.4 Mechanistic levels are not causally related to one another6.4 Levels of mechanisms in relation to other kinds of levels7 Conclusion