John of St. Thomas, the Spanish theologian and philosopher, was born John Poinsot, the son of an Austrian, at Lisbon, Portugal, and died at Fraga, Spain. When he entered the Dominican order he took his name from St. Thomas Aquinas. John studied philosophy at Coimbra, Portugal, and theology at Louvain, taught philosophy and theology in Dominican houses of study, at Alcalá de Henares (1613–1630), and from 1630 to 1643 was a professor at the University of Alcalá. Apart from certain Latin and vernacular works of devotion, his writings consist of two series of textbooks, one in philosophy, the Cursus Philosophicus (which comprises "Ars Logica," covering logic, and "Philosophia Naturalis," on natural philosophy), the other in theology, the Cursus Theologicus (a systematic commentary on Thomas's Summa of Theology).

The "Ars Logica" is fundamentally Aristotelian logic, but John developed the content of the course in...