"Why are kind relations and part relations so fundamental to our conceptual system? In addition to the organizing power of the hierarchies they form, these two sets of relations are important because they specify the constituents of the world. Ontology is the branch of philosophy (and cognitive science!) that asks what fundamentally exists, and ontological questions usually concern with kinds of things exist. Moreover, given an account of the kinds of things there are, which translates immediately into a hierarchical organization, we naturally want to ask: of what are the objects of these kinds made? The answer to this question requires consideration of the parts, generating the part-hierarchy that also organizes our concepts. Thus the major role that kind-hierarchies and part-hierarchies play in our conceptual system is not accidental but reflects fundamental ontological questions. Knowledge of parts is relevant to knowledge of kinds."

Slots and Values
ref	p32
source	Unnamed