 The first role will not be necessary if one thinks that there is a ‘master property’ of which the others are modes, or if one thinks that unity can come from some causal or organisational connection. (ii) will not apply to a tropist theory, or if one thinks that location will do the job. (iii) rests on the intuition that no collection of properties could, in themselves, amount to a substance: the very idea is a category mistake, and only the presence of a special ‘substantializing’ element could do that. It might be argued that this intuition begs the question against the bundle theory. At the current state of the debate, it looks as if there is no compelling reason for accepting substratum.