A social scientist writes, “I just read an article in Public Interest in which the philosopher Edward Feser says Thomists ‘deny there will be non-human animals in heaven.’ Now, I understand the argument that animals on earth won't be resurrected in heaven. But he seems to be saying more.”
I’m not sure whether Feser intended to imply more in his fine article, but let’s review Thomas Aquinas’s argument. A soul is the formal principle, or pattern, which makes the difference between a lump of dead flesh and an embodied life. In this sense all living things have souls, but they do not all have souls of the human sort. Our souls are rational; animal souls, like those of dogs, are merely sensitive.
Now everything which the merely sensitive soul does pertains to its union with the body. But the rational soul has certain purely intellectual, non-material operations which are not dependent on its union with the body, and belong to the soul in itself. St. Thomas concludes that the soul of the dog has nothing that could survive the death of its body, but the soul of a human being does.
I think this argument is correct as far as it goes, but I would qualify it in two ways. First, it doesn’t preclude the possibility of heavenly animals which had never existed in this life – and I don’t think Feser meant to imply that it did. It is only about the resurrection of animals which have existed in this life.
Second, it does not absolutely preclude animal resurrection. It only prevents us from saying that sensitive souls have something which could survive the death of their bodies by their very natures. So far as we know, God could gratuitously preserve them by means which exceed their natural powers – just as we believe He will raise redeemed humans to the vision of Himself by means which exceed our natural powers. We simply have no information on this point.