Formal Proper Parts through Strong Supplementation: A Reply to Bennett

Kathrin Koslicki argues that ordinary material objects like tables and motorcycles have formal proper parts that structure the material proper parts. Karen Bennett rejects a key premise in Koslicki's argument according to which the material ingredient out of which a complex material object is made is a proper part of that object. Koslicki defends this premise with a principle motivated by its power to explain three important phenomena of material composition. But these phenomena can be equally well explained by a weaker principle that does not support the questioned premise in Koslicki's argument, Bennett argues. I show that Bennett's weaker principle, together with an appropriate strengthening of a different premise in Koslicki's original argument, still yields a sound argument for the existence of formal parts.