The Wars of Religion 655 have forgiven Galileo if he had confined his discussions to the learned who could read Latin, but they thought it highly dan- gerous to have the new ideas set forth in such a way that the people at large might find out about them and so come to doubt what the theologians and universities were teaching. Galileo was finally summoned before the Inquisition and some of his theories condemned by the church authorities. ( -. ^ Just as the Thirty Years' War w^as beginning, a young French- Descanes man by the name of Descartes had finished his education at a Jesuit college and decided to get some knowledge of the world by going into the war for a short time. He did much more thinking than fighting, however. Sitting by the stove during the winter lull in hostilities, deep in meditation, it occurred to him one day that he had no reason for believing anything. He saw that everything that he accepted had come to him on the authority of some one else, and he failed to see any reason why the old authorities should be right. So he boldly set to work to think out a wholly new philosophy that should be entirely the result of his own reasoning. He decided, in the first place, that one thing at least was true. He was thi7ikifig, and therefore he must exist. This he expressed in Latin in the famous phrase Cogit-o, ergo SU7TI, " I think, therefore I am." He also decided that God must exist and that He had given men such good minds that, if they only used them carefully, they would not be deceived in the conclusions they reached. In short, Descartes held that clear thoughts must be true thoughts. Descartes not only founded modern philosophy, he was also Work of DcscsTtc s greatly interested in science and mathematics. He was impressed by the wonderful discovery of Harvey in regard to the circulation of the blood (see below^, p. 661), which he thought well illustrated what scientific investigation might accomplish. His most famous book, called An Essay ofi Method, was written in French and addressed to intelligent men who did not know Latin. He says that those who use their own heads are much more likely to reach the truth than those who read old Latin books. Descartes
