In this thesis, I provide a scientifically informed defence of metaphysical emergence, the idea that some systems are metaphysically distinct from their constituent parts and possess properties that are not reducible to their parts’ properties. Moreover, I argue that metaphysical emergence is acceptable only if embraced wholeheartedly, along with all its ontological corollaries. Finally, I offer an ontology that suits metaphysical emergence.

I begin, in chapter 1, by rejecting a computational class of theories of emergence that I take to be the most important rivals to metaphysical emergence. These theories try to explain the irreducible properties of emergent phenomena by reference to their computational irreducibility. I show that computational irreducibility fails to fulfil its philosophical roles in these theories.

In chapter 2, I offer a practical argument in support of metaphysical emergence. The main message is that the growing reliance on so-called irrational scientific methods provides evidence that objects of science are indecomposable and as such, are better described by metaphysical emergence as opposed to an alternative reductionistic metaphysics.

In chapter 3, I analyse the emergentist research programme in linguistics as an example of the scientific application of the concept of emergence. The underlying theme of this chapter is that half-hearted emergentism is hopeless. I show that if one adopts some weak understandings of the concept of language emergence, the emergentist programme is not fundamentally different from the other non-emergentist research programmes in linguistics. On the other hand, if one adopts some stronger understandings of emergence then the programme would have a unique character, but at the cost of some philosophical corollaries that demand a fundamental revision of the emergentist programme in its present shape.

In chapter 4, I suggest that if one accepts metaphysical emergence, then one needs to revise one’s ontological views as well. I compile the minimum set of ontological commitments necessary for maintaining the metaphysical and causal claims of structuralist accounts of metaphysical emergence. The set has three elements: (A) structural realism, (B) structural causation, and (C) the condition of downward percolation.