Rationalism is the belief that reason, not experience, is the most important source of knowledge. It is a direct contrast to empiricism, which is a theory that experience is the most important source of knowledge in the world. From this belief, there are three distinct types of knowledge that a rationalist could use as supporting his beliefs.
Rationalists may argue that humans posses a form of innate knowledge. As opposed to the belief that humans are born with minds like blank slates, rationalists believe that we are born with certain basic instincts. It is also believed that we are born with the ability for certain concepts, such as the faculty for language.
Secondly, rationalists also argue that there are some truths that can be figured out without world experience. Some examples of this are mathematics, logic, or ethical truth. They believe that we have the ability to tell the difference between right and wrong without having to base that knowledge in experience.
The rationalists also argue there are some truths that, although grounded in experience, cannot be derived from experience alone. One example of this is aesthetic truths. For example, two people can observe the same object and conclude contradictory opinions of its existence. This proves that aesthetic qualities do not present themselves to our senses, but instead are born from experience by reason. Also, we do not see causation, we only observe one event and then another. Rationalists believe it is the mind, not the world, that gives us the idea that the former causes the latter.
Rationalism is not a modern basis of philosophy; rather, rationalist thought dates back to 570 BCE. Pythagorus was discovered to be one of the first philosophers to stress rationalism. Although he was a great mystic, mathematician, and scientist, it has been said that he was one of the first men known in history to call himself a philosopher. Other rationalists throughout history were Plato and Aristotle.
Modern rationalists, such as René Descartes, developed popular rationalist thought that is used today. Descartes held the belief that only knowledge of eternal truths, are attained by reason alone. Some other knowledge, such as physics, is aided by scientific method. Other modern rationalists include Baruch Spinoza, Gottfried Leibniz, and Immanual Kant.
Even though rationalism has roots that date back to the dawn of recorded history, many of its beliefs and theories still hold true today. The basis of rationalism is still taught in many philosophy classes throughout the world.