This succession of men included Saint Anselm, who posited that God's existence was largely provable in the very definition of Him as 'that than which nothing greater can be conceived.'
It included Peter Abelard, a teacher who gathered a list of apparent contradictions in Church teaching and the Bible. He then set his students to the task of resolving them, saying to them "By raising questions we begin to enquire, and by enquiring we attain the truth, and, as the Truth in fact said: 'Seek and ye shall find, knock and it shall be opened to you.'"
It included Peter Lombard, who may have been a student of Abelard, and whose work 'Sentences' became, next to the Bible, the central textbook of theology for five hundred years, from the late 12th thru the 17th centuries. This systematic exposition of Catholic faith looked to combine reliance on Church authority with the employment of reason in order to explain theological points.
The work done in this 'Age of Scholasticism' is explored in more detail in an excellent recent book by Thomas E. Woods, Jr. called 'How the Catholic Church Built Western Civilization'. Woods speaks of the Scholastics, who emerged during the period of history that we know as the 'Middle Ages', as educated men.
These men "wanted students to be able to detect logical fallacies and to be able to form logically sound arguments." They did this work within the newly developed 'University' system, which the Church had itself developed to expand the studies of those who showed "consistent interest in the preservation and cultivation of knowledge."
In his work called the 'Summa Theologiae', Thomas Aquinas "raised and answered thousands of questions in theology and philosophy." Saint Thomas stated in this work that the existence of God could be known through both reason and divine revelation, and developed five ways for demonstrating this existence. He ultimately found that God is the 'Uncaused Cause', or that one thing that is not in itself in need of something else to cause its existence.
The Summa's topics are said to follow a pattern: from God' existence, to God's creation, to Man, Man's purpose, Christ, the Sacraments, and finally back to God. In the Summa, Aquinas cites great thinkers from not only the Christian world, but also from the Muslim and Jewish spheres, and ancient scholars such as Aristotle.
The Summa Theologiae was the greatest theological statement of the entire Middle Ages, and was left unfinished when Saint Thomas Aquinas died in 1274AD. It is to works like this, developed, inspired, and supported by the Catholic Church and its scholars, that the modern world owes an undeniable, inarguable debt.
Ultimately the creation in the Middle Ages of the university, the commitment to reason and rational argument, and an expanded spirit of inquiry amounted to what Woods characterizes as "a gift" to mankind "whose center was the Catholic Church."
Anyone with interest in history, especiallyl in the undeniable influence of the Catholic Church in the development of western civilization, should read Woods' book. It is great as church history, but tremendous as pure historical reading as well.