Plato:
Plato thought there was one universal kind of justice and truth, and to be just, one must be smart. His truth theory taught that there are four degrees of truth: imagining, believing, understanding, and reasoning. Imagining and believing are shallow forms of truth, while understanding and reasoning are higher levels of truth. To reach the higher levels of truth, one must make balance with the three parts of his soul: reason, spirit, and desire. They are constantly in conflict with one another and must be balanced out to achieve true happiness. Finally, Plato’s political philosophy is centered on the idea of the philosopher-king, someone who was “truly” just (chosen by a series of tests) who could have total rule over everyone else, those who weren’t as smart and therefore not as just as their leader.
Descartes:
Descartes’ philosophy revolved around the idea of the mathematical proof. To prove an idea, he needed to start with something he knew to be true and work from there. His goal was to find truth in life, and meditated to do so. In his meditations, he doubted everything in order to decide if they were real or not. As he went further into his meditations, he began to see everything as false and only his mind as real. He finally came to the conclusion that if he was doubting his existence, something must be causing that doubt, so his existence is real. This is where the term “cogito ergo sum” comes from: I think; therefore, I am. Through this same process, he came to the conclusion that God exists, because in order for him to doubt God’s existence, he needs something to spark those thoughts.
Hume:
Hume believed that moral beliefs only express feelings and emotions, and should not be taken for rationale. He also believed in the idea that all ideas are not connected and do not directly lead to something else; humans have made the idea of cause and effect up in our heads. He also thought that knowledge only comes from the senses and the experiences...