Thomas Aquinas (c. 1227-74) was the greatest of medieval philosophers and theologians. From Albertus Magnus he learned the Aristotelian theory of knowledge derived from reason, but to it he added his own concept of the higher knowledge derived from revelation. All of his writings develop this quality, but in the Questiones of the Summa, his last and greatest work, the nature, attributes, and relations of God and man were discussed. His teaching was decreed by Leo XIII to be the basis of Catholic theology; it underlies all subsequent political and social inquiry into the position of man in the state or in the universe. The first complete edition appeared in Basel in 1485.[PMM]