Economics is the study of the "economic world' of human action in relation to material resources. The economic world is therein composed of objects: including economic agents (e.g. Homo Oeconomicus, firms), resources (e.g. commodities), economic institutions (e.g. markets, money, central banks); yet is also composed of knowledge (e.g. technology, expectations, routines, preferences) and is thus in significant part subjective. The fusion of object and subject, and the complexity this raises (for example in the theory of value), however, is just the beginning of the vast ontological complexity of the economic world. For the economic world is also an emergent (and massively parallel) process of socially-coordinated individual knowledge. This knowledge is pragmatic, conjectural and mostly inductive. The organizations and institutions that coordinate economic behavior are themselves subject to self-organization and evolution. There is manifold supervenience and protean sets. The question "What is the economic system made of?' or "What are the constituents of economic reality?' has a great many possible answers that harbor substantial incommensurability. The upshot, then, is that the economic world is ontologically complex in a profound way.