Cogito, ergo sum. Background Hello, my name is Akihiro Ono, and today I’d like to talk about Rene Descartes and his though experiment, “Cogito, ergo sum.”. “Cogito, ergo sum.” is Latin language. In English, it is expressed as “I think, therefore I am”. In Japanese, it is expressed as "Wareomou,yueniwareari".　 Descartes, a French philosopher, tried to doubt the various things in this world. For example, an apple there may be a hallucination, and the one I am studying here may actually be a dream, and the back of a person who is facing me now may not exist. Then Descartes noticed most things, including myself of this world can doubt. So, Descartes thought that are there certainly existence which cannot be doubted? And he summarized that, and in 1637 issued the book "Discourse on the Method". Next, I will talk about the conclusion that Descartes has issued. Research Question What is truly real in the world? Methods & Data The process until Descartes arrives at the conclusion is as follows. 1. First he tried to doubt the various things in this world. 2. And he thought there was a certain thing that cannot be doubted. 3. He was able to doubt most things. 4. But he could not doubt that there was something suspicious. 5. Therefore, when he was thinking about that, he realized that he could not doubt that there was someone who was suspicious. Conclusions and Future Research This discovered by Descartes had a great influence on future philosophers. And the word "Cogito, ergo sum." is still famous now. thank you for listenning,