 While there is a shared core of concerns in these last two approaches, it is clear that in addition to the superficial difference that Belnap and Müller restrict “sortal” to approximately the substantial sortals as defined in Guarino et al. 1994, there are differences even in the area of overlap. Modal rigidity and modal constancy are very similar. (Some caution is necessary here since the modal logic frameworks differ.) But Belnap and Müller emphasize modal separability and do not mention a counting requirement, Guarino et al. (1994) require countability but are not concerned with modal identities.