In the De potentia, Thomas Aquinas runs a series of disputations on the power of God. The treatise considers ten questions related to God's power to create external things, namely the universe, angels, and human beings. His explanation of creation here is the most developed treatment found in any of his writings, but the principal purpose of the work is to analyze the internal life of God--that is, the Trinity. According to Aquinas, we predicate the Persons of the Trinity as relations, not as absolute things, and he examines the processions of the Son and the Holy Spirit in the light of reason.
The complete De potentia is a very long document. In this new translation, Fr. Richard Regan offers an abridged version that passes over some of the full text while retaining what is most important when it comes to following the flow of Aquinas's thought.