Rationalism
Rationalism is the view that reasoning by itself is a source of knowledge or proof. It is a philosophical movement that began in the 17th century, but the same ideas were also talked about before then. Rationalist philosophers believe that all knowledge can be understood through a process of reasoning, without any external sources. They do not believe that human beings can understand everything this way, but that it is theoretically possible. Rationalist philosophers attempt to understand ideas like God and the soul in this manner.