How did Thomas Aquinas view grace as opposed to the church fathers? I talked to a teacher at a theological seminary here in Sweden today, and we discussed the nature of grace: Fulfillment of natural potential or completely otherworldly? His idea was that with Thomas Aquinas (and probably "et al" in his era) there was a change in how grace is viewed: It became detached from our natural potential and God's work in creation. can anyone weigh in on this?
First, I must state that I am, by no means, authoritatively/formally trained on the subjects of Thomistic theology, the writings of the Early Church Fathers, nature and grace, or any combination of each.  I only hope that this might be somewhat of a starting point for much more expansion.  This is such a massive subject and could easily fill the pages of many books. I am being as brief as possible with the hope that someone more qualified will (and should) supplement or replace this answer.

Many Church Fathers taught about the relationship between nature and grace, and to compare St. Thomas to individual teachers of the early Church would take a tremendous amount of labor. There are, however, 2 “Champions of Grace” that rise up above the rest in the eyes of both secular and Christian scholars – St. Gregory of Nyssa in the East, and St. Augustine of Hippo in the West.  These 2 Fathers seem to epitomize their own eastern and western schools of thought. St. Gregory was influenced by Origen and St. John Chrysostom, whereas St. Augustine studied under St. Ambrose.

SS. Gregory, Augustine, and Thomas all viewed nature through the “lens” of Aristotle’s “categories.”  However, there are apparently 2 closely related characteristics between SS. Thomas and Augustine that drastically differ from St. Gregory in the East.


Both view Grace and Nature as intertwined due to necessitated contingency.
Both view Nature as corrupt from the fall of Man, and therefore must be redeemed by God’s Grace.



  Gregory, like Aristotle, distinguished between the category of
  substance and the other categories–relation, quality, quantity, place,
  time, action, passion (Categories 1 – 9). In themselves, qualities are
  ideas in the mind of God. But they can also be projected out from God;
  and when that happens, they become visible. Now Gregory observes that
  although we ordinarily speak of these immanent qualities as inhering
  in substances, all we really perceive are the qualities of things, not
  their substances. It is but a short step to the conclusion that a
  physical object is nothing more than the convergence of its qualities.
  Thus matter as such doesn’t really exist; bodies are really just
  “holograms” formed by this convergence of qualities. Consequently
  there is no problem of how an immaterial God could have created a
  material world, for the world isn’t material at all. (1)


St. Gregory explicitly uses the term “energies” to cover those qualities that are immanent in the physical world. Energies are the “powers” and “movements” by which substances are “manifested”; the energy of each thing is its “distinguishing property” (idioma).  Gregory goes so far as to assert that apart from its energies a nature not only cannot be known, but does not even exist. 


  Even the inquiry as to that thing in the flesh itself which assumes
  all the corporeal qualities has not been pursued to any definite
  result. For if anyone has made a mental analysis of that which is seen
  into its component parts, and, having stripped the object of its
  qualities, has attempted to consider it by itself, I fail to see what
  will have been left for investigation. For when you take from a body
  its color, its shape, its hardness, its weight, its quantity, its
  position, its forces active or passive, its relation to other objects,
  what remains that can still be called a body, we can neither see of
  ourselves nor are taught by Scripture. . . . Wherefore also, of the
  elements of this world we know only so much by our senses as to enable
  us to receive what they severally supply for our living. But we
  possess no knowledge of their substance . . . . (2)


St. Gregory diverged from SS. Augustine and Thomas by viewing nature as nothing more than “qualities” emanating from the mind of God.  SS. Augustine and Thomas believed that God purposely creates material elements, such as wine, bread and water, to convey supernatural grace.

St. Augustine’s view of Grace was heavily influenced by his correspondence with Pelegius .  Pelegius taught that original sin did not taint human nature and that mortal will is still capable of choosing good or evil without special Divine aid. Thus, in contrast to 1 Corinthians 15:19-22 (especially verse 22), Adam's sin was "to set a bad example" for his progeny, but his actions did not have the other consequences imputed to original sin. Pelagianism views the role of Jesus as "setting a good example" for the rest of humanity (thus counteracting Adam's bad example) as well as providing an atonement for our sins.  

St. Augustine fought against the Pelegian heresy by developing the doctrine of grace and free will, therefore earning the title, “Doctor of Grace.”  Contrary to what was taught by Pelegius, St. Augustine said that Man’s nature was “at first faultless and without sin,” but through the sin of Adam, became corrupt so that nature was “darkened and weakened.” 


  Man's nature, indeed, was created at first faultless and without any
  sin; but that nature of man in which everyone is born from Adam, now
  wants the Physician, because it is not sound. All good qualities, no
  doubt, which it still possesses in its make, life, senses, intellect,
  it has of the Most High God, its Creator and Maker. But the flaw,
  which darkens and weakens all those natural goods, so that it has need
  of illumination and healing, it has not contracted from its blameless
  Creator— but from that original sin, which it committed by free will.
  Accordingly, criminal nature has its part in most righteous
  punishment. For, if we are now newly created in Christ, 2 Corinthians
  5:17 we were, for all that, children of wrath, even as others,
  Ephesians 2:3 but God, who is rich in mercy, for His greatlove
  wherewith He loved us, even when we were dead in sins, has quickened
  us together with Christ, by whose grace we were saved. Ephesians 2:4-5
  (3)


St. Augustine’s development of grace and nature foreshadowed that of St. Thomas’ in the sense that Man’s nature had to be redeemed.  


  This grace, however, of Christ, without which neither infants nor
  adults can be saved, is not rendered for any merits, but is given
  gratis, on account of which it is also called grace. Being justified,
  says the apostle, freely through His blood (Romans 3:24). Whence they,
  who are not liberated through grace, either because they are not yet
  able to hear, or because they are unwilling to obey; or again because
  they did not receive, at the time when they were unable on account of
  youth to hear, that bath of regeneration, which they might have
  received and through which they might have been saved, are indeed
  justly condemned; because they are not without sin, either that which
  they have derived from their birth, or that which they have added from
  their own misconduct. For all have sinned— whether in Adam or in
  themselves— and come short of the glory of God (Romans 3:23) (4)


Here, St. Thomas seems to be echoing the Doctor of Grace:


  It is befitting Holy Scripture to put forward divine and spiritual
  truths by means of comparisons with material things.  For God provides
  for everything according to the capacity of its nature.  Now it is
  natural to man to attain to intellectual truths through sensible
  things, because all our knowledge originates from sense. (5)


For a more in-depth exposition on St. Thomas' emphasis on the necessary perfection of nature by grace click here.

Augustine upheld the early Christian understanding of the Real Presence of Christ in the Eucharist, saying that Christ's statement, "This is my body" referred to the bread he carried in his hands, and that Christians must have faith that the bread and wine are in fact the body and blood of Christ, despite what they see with their eyes. St. Thomas’ doctrine of Transubstantiation only builds upon and clarifies the importance of the roles of nature and grace propounded by the Western fathers.  

In my mind, if there was ever a divergence by St. Thomas from any of the Fathers, it would be due to the trickled down differences of the Eastern and Western Fathers on the subject of substance and matter.  Perhaps if we could look back into the history of the early Church with the Summa Theologica as our guidebook, we would be pointed more in the direction of the West than of the East. 

Frank Sheed summarizes the similarities of SS. Thomas and Augustine in his great work Theology and Sanity:


  Religion is the act of man — the whole man, soul and body. It is not
  the act of the soul only, for man is not only soul . . . The
  supernatural does not ignore the natural or substitute something else
  for it. It is built upon or built into the natural. Sanctifying grace
  does not provide us with a new soul; it enters into the soul we
  already have. Nor does it give the soul new faculties but elevates the
  faculties that are already there, giving intellect and will new powers
  of operation. God-as-Sanctifier does not destroy or bypass the work of
  God-as-Creator. What God has created, God sanctifies. (7)


I am, by no means, in a position to make conclusions about the differences and similarities of St. Thomas and the Church Fathers.  However, it appears to me that St. Thomas didn’t fall too far from the Western tree.  He does, in certain passages, seem to echo what St. Augustine taught. Like Augustine and Ambrose before him, St. Thomas further develops the idea that grace does not destroy nature, but efficaciously redeems it.  Both SS. Augustine and Thomas emphasized the necessity of the sacraments, which by definition are natural channels of supernatural Grace.  


http://www.iep.utm.edu/gregoryn/
Against Eunomius II [949]
http://www.newadvent.org/fathers/1503.htm
http://www.newadvent.org/fathers/1503.htm.
Hyman, Arthur, and Walsh, James J.  Philosophy in the Middle Ages : The Christian, Islamic, and Jewish Traditions.  Indianapolis:  Hackett Publishing Co., 1973.  Second Edition.
Theology and Sanity, 300-301