Session Notes

What We Will Learn Today

  1. What rationalists believe about knowledge
  2. Who the major philosophical proponents of rationalism are
  3. What rationalists think about experience
  4. How rationalism has fared in contemporary philosophy


The word “rationalism” is notoriously used in different ways, by various thinkers. It has also changed meaning slightly over the centuries. For this course, we will define rationalism by identifying four contours.

Four Contours of Rationalism

  1. First, rationalists believe that reason, not sensory experience, provides reliable knowledge about the world.
  2. Second, rationalists prefer deductive inference, rather than induction. Remember that deduction argues from the universal to the particular. It starts with general principles and applies these principles to particular instances.
  3. Third, rationalists believe that the knowledge we gain through deductive inference provides a unified system. Sometimes this system is called a worldview, or a comprehensive paradigm.
  4. Fourth, rationalists hold that everything we do experience can be understood in terms of this unified system.
  5. In all of this, rationalists tend to be optimistic about the ability of the human mind to make sense of the world and are confident that reason can overcome the confusion people have about truth. This confusion they believe is often caused by mistakes we make when we observe the natural world or when we allow irrational emotions to cloud our judgment.

Platonism and Rationalism

  1. Remember that “epistemology” is the theory of how we know what is true.
  2. Plato explained his distrust of experience and human opinion in his work called the Phaedo.
  3. Perhaps one reason for his perspective is that Plato’s beloved teacher, Socrates, was condemned to death by people who allowed their experiences and emotions to produce inconsistent opinions. These human opinions condemned an innocent philosopher to death. Reason, on the contrary, is not subject to the whims of popular sentiment.
  4. In the Phaedo dialogue, as usual, Plato uses Socrates to convey his ideas.
  5. Socrates explains that philosophers are supposed to be concerned with the soul, not the body. The body engages the world through the senses. The soul engages the world through reason.
  6. Unlike modern neuroscientists, who are finding that our physical bodies and our minds are interconnected, Plato believed that there was rigid separation between mind and body. He believed that the body could provide no reliable information to the mind. On the contrary, the body only served to trick our minds into believing falsehoods.
  7. Plato provides an example, using a stick and a pool of water. When we put a stick into water, it appears to bend. When we take the stick out, it is straight again. Does this mean the water is bending the stick? Of course not. Rather, the light hits our eyes at a different angle when it passes through water, creating an optical illusion. Plato believed that because the senses are so prone to illusion in this way, pure reason can help us avoid making mistakes about what is true.

Many famous philosophers history are associated with this rationalist tradition, though each had a slightly different understanding of the role of the senses. You don’t need to know the particular approaches of each of these thinkers. Instead just remember their names so that, as you read about them in the textbook, or hear their names in discussion, you will know that they fall into the rationalist camp.

These Rationalist Thinkers Include

  1. René Descartes (1596-1650)
  2. Gottfried Wilhelm Leibniz (1646-1715)
  3. Baruch Spinoza (1632-77)

Rene Descartes:

  1. The most famous of the Rationalists
  2. The title of his best known work is Discourse on Method for Conducting One’s Reason Well and For Seeking the Truth in the Sciences.
  3. In part two of this work, he says that when he was in Germany during the Thirty Years’ War, the cold winter caused him to shut himself up for an entire day in a stove-heated room. He writes, “I was completely free to converse with myself about my thoughts.” This illustrates the nature of the entire work.
  4. No observation or experimentation was involved in the formulation of his system. Instead, he was alone with his rational processes
  5. During this time, he doubted everything he had been told by authorities, and he doubted the opinions he had based on intuition or sense experience.
  6. To find something that was certain—and free from all doubt—he built his philosophy on one thing he knew to be true. He said, “I think, therefore I am.”
  7. Based on the foundation of this one truth he used deductive reason to build a structure of knowledge.

Reasons For the Decline of Rationalism

  1. First, a philosophical perspective called empiricism, which took a distinctly different approach to epistemology, contributed to the development of modern science, which relies on a scientific method rooted in observation of the world we experience. Science was so quickly successful that its technological benefits seemed to vindicate an empirical approach to the natural world.
  2. Second, in Western history, rationalism led to a sort of intolerance toward those who seemed to be irrational or opposed to a giant, rational system of belief. To give just three examples, those who opposed the French revolution, the Nazis, or the Stalinists were all punished for being immoral. After all, if one believes a system to be rationally certain, anyone who opposes it must be doing so because of bad motives, not an honest difference of opinion.
  3. Third, neuroscientists have not discovered any a priori or innate knowledge in the human mind.

It’s worth spending some time clarifying the term “rationalism” itself.

  1. Sometimes, it has been used to describe a rejection of religious beliefs. Because many religions are based on special revealed words from God through a prophet, the lack of rationalist support for such things meant that religion was irrational, and unworthy of a thinking person.
  2. In this sense, “rationalism” can mean “secularism,” or “anti-supernaturalism.”
  3. Descartes himself believed that his rationalist method led belief in the existence of God, so rationalism does not always lead to atheism.
  4. But, in the modern era, it did lead to a view of God called “Deism”, which is the belief that an intelligent designer set the world in motion, but does not have a personal relationship with humans, does not intervene through miracles, and does not hear prayers.

Christian Reflection

  1. Precisely the overconfidence in human reason that Luther found problematic.
  2. Paul in Romans 1:18 “For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth.”
  3. We suppress the truth in unrighteousness.
  4. Jonathan Haidt, in his book The Righteous Mind argues that we typically live according to our physical desires and our will and tend to use reason merely to defend what we are subjectively already committed to.

Christian Reflection Continued

  1. More importantly, the world is hard to predict. Christians throughout history have emphasized the empirical, embodied, and particular nature of Jesus of Nazareth, not abstract rational ideas, as the basis for their faith.
  2. Even pre-Christian Jewish theism tended to emphasize God as a person in relation with Abraham, Isaac, and Jacob rather than as a rational abstraction.


  1. Rationalists emphasize the importance of seeking knowledge through a priori reason, believe that we are born with at least some innate knowledge and use deductive reasoning to develop a unified system of knowledge.
  2. The three most important philosophical proponents of rationalism, after Plato, are Descartes, Spinoza, and Leibniz.
  3. Rationalists tend to distrust experience, since the senses are often unreliable.
  4. Because of the success of modern science and the scientific method, rationalism has fallen out of favor in most philosophical circles,
  5. Christianity teaches that human rationality is both finite and fallen; for this reason, pure reason is often viewed with.

Further Reading:

  1. Plato, Phaedo
  2. Descartes, Discourse on Method