 Hempel and Oppenheim also object that Emergentists are erroneously committed to regard the mass or weight of a whole as an emergent property. (Weight is, of course, a reducible characteristic if there ever was one!) The reason they give for this is that not even the weight of a whole can be logically inferred from premises that solely contain propositions about the weight of the parts; in addition a law is needed which expresses the weight of the whole as some specific mathematical function of the weight of the constituent (1948, p. 119). However, Broad’s account clearly anticipates the objection. He provides the reason why a property such as weight (or mass) should not be conceived as an emergent property. To “explain the behaviour of any whole in terms of its structure and components we always need two independent kinds of information. (a) We need to know how the parts would behave separately. And (b) we need to know the law or laws according to which the behaviour of the separate parts is compounded when they are acting together in any proportion and arrangement” (1925, p. 61; Broad’s italics). So to know about the mass of a whole X we need to know the mass of X’s parts and the principle according to which the mass of a whole is determined by the mass of the parts. It is through experience that we have found that the mass of a whole is the mathematical sum of the mass of the parts; and it is through experience we have found that the very same principle (or law of composition) is applicable to any type of whole. To see this, consider the last clause of Broad’s characterisation of emergent properties above. The clause says that an emergent property of a certain whole cannot, even in theory, be logically inferred from the most complete knowledge of the properties of the parts in isolation or in other wholes which are not of the form to be found the whole in question. Is this applicable to the mass of a certain whole? Is it applicable to the mass of X? No, certainly not: we are able to logically infer the mass of any whole, including X, from knowledge of the masses of parts in isolation or in wholes other than X.