Quaeritur: I was listening to a conference given by Fr. Gregory Hesse (now deceased). He spoke about the image of God in man, that is, the intellect and will. However, he said that St. Thomas Aquinas missed the boat when he said that there are only two powers in the human soul. As there are three persons in the Blessed Trinity, it is only sensible that there are three powers of the human soul to reflect the Holy Trinity. Fr. Hesse said that this third power is what we can call the “heart’ or “fire.” Its object is the “beautiful,” whereas the object of the intellect is the “truth” and the object of the will is the “good.” He basically stated that this third power is the principle/means of charity (love). Fr. Hesse seemed to be very convincing. Do you know anything about this supposed third power?
Respondeo: Yes, this idea was first proposed by Dietrich Von Hildebrand. He was motivated by a serious misunderstanding of St. Thomas' doctrine on the will. For Aquinas, the will does more than just choosing. It also does other acts, such as intention, fruition, command, consent, love, etc. But Von Hildebrand in his works Ethics and The Heart, appears to be under the impression that the only thing the will does in Aquinas is choose. For this reason, he felt the need to posit a third power, the 'heart', which could do such acts as "respond to value"---everything that he thought Aquinas' 'will' could not do. Yet Aquinas accounts for this type of activity (and lots more) with multiple powers, including the will and the passions. In this respect, then, Fr. Hesse was not being a Thomist.
The issue is quite complicated. I intend to publish a refutation of Von Hildebrand on this in the near future. For now, I recommend you take a good look at ST I.81-83 and I-II.6-17. I am also working (long term) on a book whose primary aim will be to refute the objections of the 'personalists' and 'phenomenologists' against St. Thomas and Thomism. This topic would constitute one of the chapters of the book.