This thesis is concerned with the theory of ontological emergence; a theory that posits a new kind of entity – usually an emergent property – that occurs in complex systems and can explain some system-level behaviour. The theory holds that these emergent entities are dependent on, but novel with respect to, the components of those systems. Such entities have been invoked to explain behaviours as diverse as symmetry breaking in molecular physics to the possibility of personal agency. As a metaphysical theory it is useful wherever there is a lack of understanding about how system-level behaviour can occur based on what we know about the parts of that system. Besides its usefulness, the theory, if true, would profoundly impact our understanding of fundamental ontology.
The first half of this thesis aims to do three things: first, identify a problem that emergence can explain; second, identify what emergence must do in order to solve that problem; third, identify a theory of emergence capable of doing it. The first and second of these aims will require us to outline issues in fundamental ontology and metaphysical methodology that are critical to any assessment of the possibility of emergence. They both also require making some commitments on these issues. Among such commitments will be a commitment to an ontology of properties as causal powers.
I argue that emergence is a theory of macro-properties and that the primary problem it solves is the Problem of Reduction. I thereafter defend the theory of causal powers emergence against charges that it is incoherent and inconsonant with science and natural unity; these and other conflicts are shown to be unproblematic once the theory is properly explicated. In these respects, this thesis finds no fault with the coherence of emergence. The key claims in the second half of the thesis instead pertain to the necessity of emergence to solve the problem that I have identified. The argument is that even if causal novelty, holistic effects and top-down causation are apparent in a system, a properly developed causal powers ontology can account for them without positing new fundamental properties. I develop an option called non-reductive inherence based on a theory of powers admitting a plurality of compositional principles. The thesis ends by expounding this alternative to emergence and setting out some of the trade-offs between the positions
