A primary concern during the Protestant Reformation was the condition of human nature following the fall of Adam, and questions arise regarding whether Adam’s guilt, sinful nature, or righteousness are passed along to his offspring, whether covenantally or seminally. It matters how we conceive of postlapsarian human nature, and this has sometimes been thought to divide Catholics and Protestants. If human nature does not remain intact after the fall, how can we still be human in a meaningful way? If human nature remains intact after the fall, then Pelagianism, or something similar, could follow. Recently Duby and Saad have compared Thomas Aquinas and Francis Turretin regarding divine attributes and natural law respectively, and they have concluded that these two scholastic theologians, while belonging to distinct traditions, overlap in thought in these areas. This paper will similarly argue that Thomas and Turretin have similar ontologies concerning post-fall human nature in that they both invoke a twofold ontological distinction. Both argue that human nature structurally remains intact in virtue of the body and soul, but human nature is also corrupt in virtue of the loss of original righteousness. To establish this thesis, I will work with Daniel Houck’s recent explication of this particular reading of Thomas which works to illuminate and alleviate tension in Thomas’s earlier work on Lombard’s Sentences and his later work, the Summa Theologiae. I will address the strict concept of human nature which remains intact for both Thomas and Turretin, and I will address how both of these theologians articulate a change in the human nature which accounts for original sin. Establishing this thesis demonstrates that Catholic, and particularly Thomistic, resources can and should be used in developing a robust theological anthropology.