Claim: The heat capacity of heterogeneous objects (separate parts made of different materials) may be well-defined and can be computed by adding together the heat capacities of the individual parts.
Evidence: The heat capacity may be well-defined even for heterogeneous objects, with separate parts made of different materials; such as an electric motor, a crucible with some metal, or a whole building. In many cases, the (isobaric) heat capacity of such objects can be computed by simply adding together the (isobaric) heat capacities of the individual parts.