Rationalism Rationalism can be defined as the position that reason alone, without the aid of sensory information, is capable of arriving at some knowledge, at some undeniable truths. Rene Descartes used the rationalist approach to knowledge to answer the question "What can I hold as true beyond any doubt?" Descartes believed that knowledge is obtained by reason, rather than perception, or relying on the five human senses to become aware of things. In other words, he believed that we could acquire knowledge about the world without having to first observe the world around us, but just by looking into our minds Descartes