De daemonibus (1): corporeality

Timotheus: How then, if they are not corporeal (μὴ σῶμα ὄντες), are they visible to our external vision (τοῖς ἐκτὸς ὄμασσιν)? 

Thracian: But my dear fellow, the demonic race (τὸ δαιμόνιον φῦλον) is not incorporeal (ἀσώματον); they operate by means of bodies and upon bodies. [...] Basil the Great, explicating the words of Isaiah: Howl ye idols, says, “demons secretly sit before idols, delighting in the pleasure of the polluted sacrifices (τῶν μιασμάτων). The same as greedy dogs come to hang around a butcher's shop, where there is blood and gore, so too the greedy demons eagerly take their pleasure from the blood and steaming fat of the sacrifices, wallowing around the altars and the idols erected to themselves. And indeed their bodies feed thereby, being made of air or fire or a mixture of the two elements.” Again, the divine Basil, an observer of invisible things that are indistinct to us, not only demons, but also the immaculate angels, contends that they are embodied as tenuous, airy, unadulterated spirits (πνεύματα). And he cites as evidence the words of David, the most famous of the prophets: “Who maketh his angels spirits; his messengers a flaming fire” (Ps. 104,4).  [...]

Timotheus: Why then are they lauded as being incorporeal in so many places in the Scriptures?

Thracian: Because with both writers outside the Church and even the earliest writers within the Church it is customary to use the term body for that which is grosser, while that which is more tenuous, that which is elusive (διαφυγγάνον) to the eye and impalpable, is wont to be called incorporeal, not only by our writers, but also by many of the pagans.

Michael Psellus, Dialogus de Daemonum Energeia seu Operatione (PG 122: 836b-837b)

trans. Alistair Ian Blyth