Catholic theology affected by the Reformation and the Council of Trent. Protestant emphasis on the Bible and rejection of the Roman primacy stimulated theologians to investigate more closely the sources of revelation in Scripture and tradition and establish the grounds for a rational apologetic in support of the Catholic claims. The first need was met by developing a system of positive theology, whereby the truths professed by Catholic Christianity were shown to be found in the deposit of faith. The Jesuits, led by St. Robert Bellarmine (1542-1621), became the main expositors of this system, as they also laid the groundwork for fundamental theology, which proves from history and philosophy the credibility of the Christian religion.
The speculative side of the science began a new era, occasioned by the challenges of Protestantism on almost every position of the Catholic Church. During the eighteen years of the council of Trent (1545-63), the combined intelligence of Roman Catholicism concentrated its efforts on so defining the nature of grace and justification, the Sacrifice of the Mass and the priesthood, the sacramental system and ecclesiastical authority, that insights were gained on which post-Tridentine writers have built an imposing theological structure. Their framework was mainly the Summa Theologica of St. Thomas Aquinas, with commentators in all the major schools of thought. Among the Dominicans was John of St. Thomas; (1589-1644), professor at the University of Alcalá in Spain, so named from his wholehearted devotion to the teachings of St. Thomas Aquinas; the reformed Carmelites edited a celebrated Cursus Salmanticensis; Franciscans published treatises of Duns Scotus, harmonized with St. Thomas; the Jesuits produced Francis Suarez (1548-1617), a dogmatic theologian famous for his works on jurisprudence which became of paramount importance for legislators on the continent and in America.