 It is now traditional within perfect being theology to distinguish, following John Duns Scotus, between pure perfections and impure, or mixed, perfections (Ordinatio 1.3.1, found in Philosophical Writings, p. 24). Pure perfections are those that do not presuppose limitation of some sort, while impure perfections do so presuppose. Only pure perfections are features that it is simply better to have rather than not to have. Impure perfections presuppose some limiting factor that sets the perfection in question – for example, membership in some natural kind. So being a frog is a relevant sort of limitation, and sets a range of features that count as perfections for instances of that kind. But it is not true of these impure perfections that it is simply better to have them than not to have them; it is not simply better to have webbed toes, a tongue attached at the front of the mouth, and so forth, though a frog in good shape will have those features.