Rene Descartes, a rationalist philosopher in the 16th century.
Rationalism is the idea that reason is the ultimate foundation of knowledge. It also includes the idea that actions and opinions should not be based on the emotions or religion but on reason and knowledge.
History[]
Mathematics is one example of rationalism because it does not require the use of senses to understand the numerical relationships.
Rationalism first developed during classical times under the influences of philosophers like Socrates and Plato. Their arguments would try to find logical inconsistencies in thinking that "common sense" may have. During those times, rationalism was the idea where reason alone is the source of all knowledge, not the senses.
In the 16th century, Descartes expanded rationalism by incorporating empiricism, which is the idea that knowledge is acquired through the senses. Unlike previous rationalists, he thought that mathematics was the only field where reason alone was the source of knowledge. He believed that the sciences also required the use of senses like observation to gain data, where reason would be used to understand it and draw conclusions. This was when it began to develop its modern form in which it represents the idea that knowledge is acquired through reason with data from the senses. Rationalists believe that reality has a logical structure to it, which can be discovered, and that the mind is able to understand some of it.