The transitivity of material constitution

In metaphysics, the view that material constitution is transitive is ubiquitous, an assumption expressed by both proponents and critics of constitution views. Likewise, it is typically assumed within the philosophy of mind that physical realization is a transitive relation. In both cases, this assumption of transitivity plays a role in discussion of the broader implications of a metaphysics that invokes either relation. Here I provide reasons for questioning this assumption and the uses to which this appeal to transitivity is put. As my title suggests, I shall focus on the case of material constitution, using a brief discussion of realization at the outset to motivate the discussion of the transitivity of material constitution at the core of the paper.