There are many candidates for the position of ultimate being: a naturalistic first cause, the God of perfect being theism, ‘the Good’ of Platonism, ‘the One’ of Neoplatonism, the fundamental mind of Idealism, etc. On the supposition that there is an ultimate being, we are thus faced with an a tricky question: Why is potential ultimate x the ultimate being and not potential ultimate y? It seems that x must have a distinctive feature that the other potential ultimates do not have if we are to make sense of this. But it cannot be any old distinctive feature. Potential ultimate z might be the only potential ultimate that is blue, but this distinctive feature of z would hardly explain why z is the ultimate being and the other candidates are not.

Now, it seems that perfection may be the sort of feature that we need, i.e. might be a feature that is both distinctive and explanatory. Perfection is plausibly unique-making (perfection may well entail being the greatest possible being) and ultimate-making (ultimacy is the sort of property a perfect being would have). Imperfection is quite unlike perfection in this regard. Not only are many potential ultimates seemingly imperfect, there is also no clear route from imperfection to ultimacy. Ultimate explanations that appeal to imperfect ultimates are thus, all else being equal, at an an explanatory disadvantage. They need some further feature f to explain why their candidate is ultimate and the rest is not.