Benedict de Spinoza's Ethics, first published in 1677, constitutes a major systematic critique of the traditional and religious foundations of philosophical thought. In it, Spinoza follows a logical step-by-step format consisting of definitions, axioms, propositions, proofs, and corollaries to create a comprehensive inquiry into the truth about God, nature, and humans' place within the universe. From these broad metaphysical themes, Spinoza derives what he considered to be the highest principles of religion and society and lays out an ethical system in which reason is the supreme value.

Few philosophers have so extensively influenced thought and language as Aristotle. His conception of the universe pervades Christian theology. Knowledge of his thought is necessary to understand Bacon, Galileo and the modern scientific view of nature, as well as Dante and many passages from Chaucer, Shakespeare, and Milton. Many phrases such as "liberal education" and "theory" contrasted with "practice" originated with this student of Plato and tutor of Alexander the Great. Writing to inform the beginner and stimulate the expert, eminent scholar A.E. Taylor presents a searching analysis of Aristotle's thought, including classification of the sciences; formal logic; theory of knowledge; matter and form; the four causes; God; physics; biology; sensation; ethics; theory of the state; the fine arts. He also considers Aristotle's provincialism, errors regarding the nervous system and astronomy, and defense of slavery.

Two years before he died, St. Thomas Aquinas, probably the greatest teacher the Church has ever known, was asked by his assistant Brother Reginald to write a simple summary of the faith of the Catholic Church for those who lacked the time or the stamina to tackle his massive Summa Theologica. In response, the great saint quickly set down in language that non-scholars can understand his peerless insights into the major topics of theology: the Trinity, Divine Providence, the Incarnation of Christ, the Last Judgment, and much more.

Written after the capture of Rome in 410 by Alaric, King of the Visigoths, St Augustine's City of God was intended as a response to pagan critics who blamed Christianity for this brutal defeat. Augustine attacks ancient pagan beliefs and relates the corruption and immorality that led to Rome's downfall, which began before Christ, before reaching his main argument: that the City of Man is perishing and only the Heavenly City of God will endure.

The Republic poses questions that endure: What is justice? What form of community fosters the best possible life for human beings? What is the nature and destiny of the soul? What form of education provides the best leaders for a good republic? What are the various forms of poetry and the other arts, and which ones should be fostered and which ones should be discouraged? How does knowing differ from believing?