All properties that exist in the world are functional properties in the sense of causal properties. The authors base a conservative ontological reductionism on this claim and develop functional reduction into a fully-fledged theory reduction through functional sub-types that are coextensive with physical types, providing case studies from biology. '[T]his book is recommended as a thought-provoking re-assessment of ontology for contemporary physics, and of functional reduction in the special sciences.' - Cliff Hooker, University of Newcastle, Australia, Notre Dame Philosophical Reviews