Descartes is a notable French philosopher of the 17^th century. He made huge contribution to both philosophy and mathematics. Discourse on Method written by Descartes is definitely one of the most influential and important works in history of modern science, as well as philosophy. At the beginning of this book, Descartes mentions that all people possess “good sense”, which is “off all things among men, the most equally distributed” (page 1). It’s very important to figure out the most precise meaning of this phrase, because it is the central premise of the following arguments. I was confused about what Descartes means at the beginning. In our common understanding, “good sense” means the ability to make the right decision about something. However, according to Descartes’s following descriptions, I got that “good sense” doesn’t mean intelligence, it means to reason, specific refers to the ability of using intelligence to distinguish truth from fiction. In this book, Descartes attempt to explain his method of reasoning. He claims that never accept anything as true or trust anything that we cannot verify ourselves based on our own observations. Because sense data, awareness, common elements of all possible experience are all dubious. I totally agree on his idea of skepticism and rationalism. Especially in study, we shouldn’t believe everything that others tell us, even knowledge from textbooks or professors. We should doubt, think and tell the truth. In applying the method, Descartes derives the basic truth of his own existence by stating the famous lines in part four “I, who was thinking this, was •something. And observing that this truth I am thinking, therefore I exist was so firm and sure that not even the most extravagant suppositions of the sceptics could shake it, I decided that I could accept it without scruple as the first principle of the philosophy I was seeking”(page 15). He claims the certainty of his own existence. If he thinks, then he necessarily exists. Cogito ergo sum (I think, therefore, I am) later become a fundamental element of Western philosophy, as it was perceived to form a foundation for all knowledge. In part four, Descartes also finds out independence of mind from the body with the lines “I was a substance whose whole essence or nature is simply to think [here = ‘to be in conscious mental states’], and which doesn’t need any place, or depend on any material thing, in order to exist. Accordingly this me—this soul that makes me what I am—•is entirely distinct from the body” (page 15). Then he goes on to prove the existence of God. He claims that God implants perception of perfection in the imperfect him by stating “•something that truly was more perfect than I was, •something indeed having every perfection of which I could have any idea, that is—to explain myself in one word—by •God” (page 16). Descartes’s philosophy is difficult for me, but it’s really interesting to follow his thought path. I feel like solving mathematic problems.