I. Definition

Rationalism is the philosophy that knowledge comes from logic and a certain kind of intuition—when we immediately know something to be true without deduction, such as “I am conscious.” Rationalists hold that the best way to arrive at certain knowledge is using the mind’s rational abilities. The opposite of rationalism is empiricism, or the view that knowledge comes from observing the outside world. However, in practice almost all philosophers and scientists use a combination of empiricism and rationalism.

Rationalism is an idea about where knowledge comes from, and is therefore part of the philosophical sub-field of epistemology.


II. Rationalism vs. Empiricism vs. Constructivism

Math provides a good illustration of rationalism: to a rationalist, you don’t have to observe the world or have experiences in order to know that 1+1=2. You just have to understand the concepts “one” and “addition,” and then you can know that it’s true. Empiricists, on the other hand, argue that this is not true; they point out that we can only rely on mathematical equations based on some experience of the world, for example having one cookie, being given another, and then having two.

Rationalism and empiricism both play a role in science, though they correspond to different branches of science. Rationalism corresponds to mathematical analysis, whereas empiricism corresponds to experiments and observation.

Of course, the best route to knowledge combines rational contemplation and empirical observation. Rationalists and empiricists agree on that; they just disagree on which one is more important or “primary.”

Constructivism is an effort to combine empiricism and rationalism. According to constructivists, we can observe the world around us and gain a lot of knowledge this way (that’s the empiricist part), but in order to understand or explain what we know, we have to fit it into an existing structure. That is, we have to construct a rational set of ideas that can make sense of the empirical data (that’s the rationalist part). Constructivism is a popular idea among teachers, who find it helpful in structuring lessons: constructivist teaching involves presenting new information in a way designed to fit in with what the student already knows, so that they can gradually build up an understanding of the world for themselves.


III. Quotes About Rationalism

Quote 1

“Many people think that the progress of the human race is based on experiences of an empirical, critical nature, but I say that true knowledge is to be had only through a philosophy of deduction . . . Intuition makes us look at unrelated facts and then think about them until they can all be brought under one law.” (Albert Einstein)

Many people think of science as an inherently empirical discipline — after all, it’s based mainly on observation and experiments, right? But there’s also a rationalist side to science as seen in this quote from Einstein. Einstein was not big on experiments or peering through telescopes. Instead, he took data that other people had collected and tried to understand it rationally (i.e. mathematically). His brilliant theories of special and general relativity were not the results of new experiments, but rather the result of applying a keen rational eye—and intuition–to existing data.

Quote 2

“Music has always been inseparable from religious expression, since, like religion at its best, music marks the ‘limits of reason.’ Because a territory is defined by its extremities, it follows that music must be ‘definitively’ rational.” (Karen Armstrong)

Many rationalist philosophers are fascinated by music, for exactly the reasons that Karen Armstrong points out in this quote. Music is intensely rational in some ways (you can analyze its structures and frequencies and find all sorts of mathematical patterns there), but it’s also extremely emotional and seems to short-circuit our rational brains. Thus, music exists right on the boundary between rational and anti-rational. Armstrong also makes the more controversial, but no less interesting, claim that religion works in a similar way, operating at the boundaries between rational thought and non-rational emotions.


IV. The History and Importance of Rationalism

Rationalism has deep historical roots; you might even say that its discovery defines the birth of philosophy in various cultures. The ancient Greeks are probably the most famous example: ancient philosophers such as Plato and Pythagoras argued that reality is characterized by some basic abstract logical principles, and that if we know these principles, then we can derive further truths about reality. (That’s the same Pythagoras who invented the famous Pythagorean Theorem — more evidence of the connection between rationalism and math.)

However, other Greeks disagreed. Aristotle, for example, based much of his philosophy on observation. He was fascinated by the natural world and spent much of his time gathering samples of plants and animals; in some ways he was the first modern biologist. This method is, of course, based on observation and therefore is a kind of empiricism.

Rationalism really took off in the Medieval Islamic world, where Muslim philosophers looked to Plato for inspiration. Plato’s rationalism proved to be extremely important to medieval Islam, which was an intensely rationalistic religion based on logical deduction. Its first principle was tawheed, or the Unity of God, and all other truths were thought to be logical consequences of that single revelation.

Both rationalism and empiricism played a major role in the Scientific Revolution. Empiricists did experiments and made observations by, for example, looking through telescopes. But many of the most important discoveries were made by rational analysis, not empirical observation. And of course, the experiments were also partially inspired by reason and intuition.


Isaac Newton developed his theory of gravity by working out the mathematical relationship between falling objects and orbiting planets. (Sometimes people say that Newton “discovered gravity,” but really it’s more accurate to say that he explained gravity.)

The debate between rationalists and empiricists was resolved to some extent by Immanuel Kant, one of the most influential philosophers who ever lived. Kant’s theory was that empiricism and rationalism were both true in their own ways: he agreed with the empiricists when he said that all human knowledge comes from observation. This, he said, is in fact the way that people learn about the world. But our observations are also based on certain innate ways of reasoning; our brains are hard-wired to make certain conclusions from observation and reason further in certain ways. So, he also agreed with the rationalists that knowledge is determined by rationality. As you might expect, many constructivists can trace their lineage back to Kant.


VI. Philosophy in Popular Culture

Example 1

In Civilization V, one of the social policy options is “Rationalism.” This social policy improves science output for your civilization and allows you to produce more Great Scientists. This makes sense since rationalism was so important in the early scientific revolution. However, the game illustrates “rationalism” with a picture of a scientist looking through a prism, presumably as part of an experiment. So the picture would fit better under the heading of empiricism rather than rationalism!

Example 2

“Vulcanians do not speculate. I speak from pure logic.” (Spock, Star Trek)

Spock is the perfect rationalist. His powerful brain can compute logical probabilities faster than any human being, and he is not distracted by pesky emotions or personal biases (at least most of the time; he is half-human, after all). He is capable of incredible feats of logic, such as playing three-dimensional chess.


Rationalism is associated with . . .





This sci-fi character is an example of a rationalist:





Rationalism is often seen as the opposite of . . .





Rationalism corresponds to which scientific activity:





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