Aquinas’ great work, the Summa Theologiae, sometimes called the Summa Theologica, was begun in 1266. In his writing, Aquinas adapted the philosophy of Aristotle to the needs of the 13th century and its theology. The title, Summa Theologiae, means the Summary or Totality of Theology. Within this Summary, Aquinas lays out the key aspects of Christian theology such as the “Five Ways” (Aquinas’ arguments for the existence of God); the divinity of Christ; the relation between reason and faith; and the principle of analogy. The last item offers a theological foundation for knowing God through creation.
Aquinas divided the Summa Theologiae into three parts. Each one of the first two parts is subdivided into two.