Aristotle (384–322 BC) was an Ancient Greek philosopher and polymath. His writings cover a broad range of subjects including physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, drama, music, rhetoric, psychology, linguistics, economics, politics, meteorology, geology, and government. As the founder of the Peripatetic school of philosophy in the Lyceum in Athens, he began the wider Aristotelian tradition that followed, which set the groundwork for the development of modern science.

Little is known about Aristotle's life. He was born in the city of Stagira in Northern Greece during the Classical period. His father, Nicomachus, died when Aristotle was a child, and he was brought up by a guardian. At seventeen or eighteen years of age he joined Plato's Academy in Athens and remained there until the age of thirty-seven (c. 347 BC). Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon, tutored his son Alexander the Great beginning in 343 BC. He established a library in the Lyceum which helped him to produce many of his hundreds of books on papyrus scrolls.

Though Aristotle wrote many elegant treatises and dialogues for publication, only around a third of his original output has survived, none of it intended for publication. Aristotle provided a complex synthesis of the various philosophies existing prior to him. It was above all from his teachings that the West inherited its intellectual lexicon, as well as problems and methods of inquiry. As a result, his philosophy has exerted a unique influence on almost every form of knowledge in the West and it continues to be a subject of contemporary philosophical discussion.

Thomas Aquinas, OP (1225 – 7 March 1274) was an Italian Dominican friar and priest who was an influential philosopher, theologian and jurist in the tradition of scholasticism; he is known within the tradition as the Doctor Angelicus, the Doctor Communis, and the Doctor Universalis.

The name Aquinas identifies his ancestral origins in the county of Aquino in present-day Lazio, Italy. Among other things, he was a prominent proponent of natural theology and the father of a school of thought (encompassing both theology and philosophy) known as Thomism. 

He argued that God is the source of both the light of natural reason and the light of faith. He has been described as "the most influential thinker of the medieval period" and "the greatest of the medieval philosopher-theologians". His influence on Western thought is considerable, and much of modern philosophy is derived from his ideas, particularly in the areas of ethics, natural law, metaphysics, and political theory.

Unlike many currents in the Catholic Church of the time, Thomas embraced several ideas put forward by Aristotle—whom he called "the Philosopher"—and attempted to synthesize Aristotelian philosophy with the principles of Christianity.

His best-known works are the Disputed Questions on Truth (1256–1259), the Summa contra Gentiles (1259–1265), and the unfinished but massively influential Summa Theologica, or Summa Theologiae (1265–1274). 

His commentaries on Scripture and on Aristotle also form an important part of his body of work. Furthermore, Thomas is distinguished for his eucharistic hymns, which form a part of the church's liturgy. 

The Catholic Church honours Thomas Aquinas as a saint and regards him as the model teacher for those studying for the priesthood, and indeed the highest expression of both natural reason and speculative theology. In modern times, under papal directives, the study of his works was long used as a core of the required program of study for those seeking ordination as priests or deacons, as well as for those in religious formation and for other students of the sacred disciplines (philosophy, Catholic theology, church history, liturgy, and canon law).

As a Doctor of the Church, Thomas Aquinas is considered one of the Catholic Church's greatest theologians and philosophers. Pope Benedict XV declared: "This (Dominican) Order ... acquired new lustre when the Church declared the teaching of Thomas to be her own and that Doctor, honoured with the special praises of the Pontiffs, the master and patron of Catholic schools."