What “Reason” Meant
When medieval writers spoke of reason, they usually had a more specific idea in mind than the modern phrase “being reasonable.” In the Latin tradition, ratio was the human power of working step by step from known things to unknown ones: comparing, defining, drawing conclusions. It was often contrasted with a higher power, intellectus, a direct grasp of a truth that needs no steps. Many thinkers pictured the soul as having both, with reasoning as the slower, human way of reaching what angels were thought to see at a glance.
This article looks at reason in that sense, as a practical tool for argument, and at the debates about how far it could go. The broader question of how reason relates to revelation is a separate theme.
A Toolkit of Logic
Reason’s chief instrument was logic, which was studied intensively in the schools. The tradition inherited from Aristotle distinguished several kinds of argument:
- Demonstration: reasoning from certain first principles to necessary conclusions. This was considered the gold standard of science.
- Dialectical argument: reasoning from widely accepted opinions, useful for debate and for testing ideas.
- Rhetoric and sophistry: persuasion that might be sound or deceptive, and which students learned to detect.
Teachers insisted on careful definition, since many apparent disagreements turned on a word being used in two senses. A well-trained master could often defuse an argument by pointing out an ambiguity. This approach shaped the scholastic method used in lectures and disputations across the medieval universities.
Senses, Mind and Experience
Most medieval philosophers using Aristotle held that human knowledge begins with the senses. We see and touch individual things, and the mind forms general concepts from them. Reasoning then builds on those concepts. This shaped how people studied natural philosophy: observation mattered, but explanations were mostly sought through causes and definitions, not through measurement as in modern science. Some scholars, such as those studying optics, did place greater weight on experiment, though historians debate how typical that was.
Confidence and Caution
Medieval thinkers varied widely in how much they trusted reason.
Anselm in the eleventh century believed that argument could display the fittingness of Christian teaching. Peter Abelard was bolder in applying dialectic, and his methods caused unease in some quarters; his teaching on the Trinity was criticized at a church council at Soissons. Bernard of Clairvaux warned that cleverness might replace humility. Such voices stressed the dangers of curiosity and pride.
In the thirteenth century, confident Aristotelians such as Thomas Aquinas defended a strong role for reason within its own domain. Others, including Bonaventure, held that reasoning without spiritual illumination was likely to go astray. Some arts masters in Paris were accused of teaching that a conclusion might be true in philosophy while false in theology. Historians debate whether anyone held such a “double truth” in so many words, and it may have been a charge made by opponents more than a clear doctrine. The condemnations of 1277 show how tense the argument had become.
Reason Under Pressure
By the fourteenth century, new questions arose about what demonstration could really achieve. William of Ockham and others examined the structure of language and logic closely, and their Ockham nominalism challenged the view that general terms point to real universal things. Some thinkers concluded that certain claims, such as proofs of God’s existence, were less certain than earlier writers had hoped, while keeping a rich use of logic in other areas. Historians see this less as a retreat from reason than as a shift toward finer tools and tighter limits.
Reason also served practical ends. Lawyers used it in canon law, physicians in diagnosis, and officials in assessing evidence. In investigations of suspected heresy, officials weighed testimony, though practices varied widely and often fell short of fair procedure by modern standards.
An Unsettled Question
No single medieval view of reason existed. There was a shared belief that human beings are rational creatures and that the world is intelligible, along with a recurring worry that reasoning can fail or become proud. Most thinkers held that reason is a gift to be used, but that it works within bounds. Where those bounds lay was the real matter of debate.