CathInfo.com

Obj. 6: Further, to beget offspring is a vital act. But this has befallen the angels in their assumed bodies; for it is related: After the sons of God went in to the daughters of men, and they brought forth children, these are the mighty men of old, men of renown (Gen 6:4). Consequently the angels exercised vital functions in their assumed bodies.

On the contrary, The bodies assumed by angels have no life, as was stated in the previous article (ad 3). Therefore they cannot exercise functions of life through assumed bodies.

I answer that, Some functions of living subjects have something in common with other operations; just as speech, which is the function of a living creature, agrees with other sounds of inanimate things, in so far as it is sound; and walking agrees with other movements, in so far as it is movement. Consequently vital functions can be performed in assumed bodies by the angels, as to that which is common in such operations; but not as to that which is special to living subjects; because, according to the Philosopher (De Somn. et Vig. i), that which has the faculty has the action. Hence nothing can have a function of life except what has life, which is the potential principle of such action.

Reply Obj. 6: As Augustine says (De Civ. Dei xv): Many persons affirm that they have had the experience, or have heard from such as have experienced it, that the Satyrs and Fauns, whom the common folk call incubi, have often presented themselves before women, and have sought and procured intercourse with them. Hence it is folly to deny it. But God’s holy angels could not fall in such fashion before the deluge. Hence by the sons of God are to be understood the sons of Seth, who were good; while by the daughters of men the Scripture designates those who sprang from the race of Cain. Nor is it to be wondered at that giants should be born of them; for they were not all giants, albeit there were many more before than after the deluge.

Still if some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men taken for the purpose; as when the demon assumes first the form of a woman, and afterwards of a man; just as they take the seed of other things for other generating purposes, as Augustine says (De Trin. iii), so that the person born is not the child of a demon, but of a man.

https://aquinas.cc/la/en/~ST.I.Q51.A3.Obj6

Mangles...  Like it.


I've not looked into any post-St Augustine saints' commentaries on the Nephilim.  Mostly because, as is normal, they would've adopted +Augustine's opinion and added no new info.  That's why Anne Catherine Emmerich's comments are so unusual - she both agrees (mentions possession) and disagrees with St Augustine (mentions fallen angels and Enoch).

My opinion is
a)  there were angels who fell during Noah's time (too much evidence for it, both from Enoch, Church Fathers and pagan civilizations). 
b)  possibly the "genetic material" for such Giants was 100% human, but enhanced/altered due to fallen angel possession/knowledge.  This would agree with St Augustine, Scripture, Enoch, Anne Catherine Emmerich, Ancient Aliens and the great X-files tv show, etc.  This theory agrees with all sources because Scripture does not say "how" such Giants were fathered, only that fallen angels were part of it.
c)  Such a theory also coincides with the future anti-christ, who will be 100% human.

And the reason this is all important?  Because Christ said "As in the days of Noah, so shall the coming of the Son of Man be".  Obviously, Christ was first talking about sin and lack of faith/religion but I also believe that we will see "signs and wonders" in the last days and also a return of giants/fallen angels/"alien" demons/etc.  Imagine what kind of technology "bump" our society could have, if fallen angels were directing the elites today?  Lots of people in govt say that "Area 51" is all about super-technology and that it's 50-60 years ahead of what we see now.  I think the "alien visitors" story will happen because it's the only way for the elites to introduce society to fallen angels, and a "new world" of futuristic technology.  In the next 10-20 years, I expect this to happen, if God doesn't intervene.