"Je pense donc je suis" by Descartes can be translated into English as "I think, therefore I am" and into Latin as "cogito ergo sum." Descartes published this phrase in his Discourse on the Method in 1637, and the idea became central to the tenets of Western philosophy. The work addressed skepticism, a philosophical school of thought that questioned whether knowing something for sure was possible. The meaning of this phrase is that the act of thinking about whether one existed was in itself proof that one did exist. There must be a self in order for the self to have this thought. Descartes wrote, "But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be something." In other words, while he wanted to believe he did not have a foundation for believing anything, the very fact that he had this belief was proof that he existed.