Angelology may be unfashionable, but in recent years it has re-emerged in America, where it flourishes under a different name as the ‘Possible Worlds’ school of philosophy whose principal concern is with problems of ‘transworld identity’. In particular, its subtlest and most uncompromising proponent, David Lewis, has developed what he calls ‘Counterpart Theory’. This is a theory of modal quantification in which a close resemblance relation is substituted for strict identity, and it would seem to be a theory well-suited to provide a logical underpinning for what has been traditionally said of angels in their role as guardians. I have no reason to suppose that David Lewis would approve of the use to which I am about to put his Counterpart theory, and what I have to say should be regarded as no more than a modest footnote to the debate now being conducted in the stratosphere of symbolic logic with all the attendant ingenuity and zeal that once characterised scholastic disputations on the subject of angels.

For example, Aquinas discusses whether ‘morning knowledge’ and ‘evening knowledge’ are the same for angels. He explains this Augustinian distinction as follows: ‘Their knowledge of the primordial being of things is called morning knowledge; and this is according as things exist in the Word. But their knowledge of the very thing created, as it stands in its own nature, is termed evening knowledge, because the being of things flows from the Word as from a kind of primordial principle, and this flow is terminated in the being which they have in themselves.’