方法序説
is a philosophical statement that was made in Latin by René Descartes, usually translated into English as "I think, therefore I am". The phrase originally appeared in French as , in his "Discourse on the Method", so as to reach a wider audience than Latin would have allowed. It appeared in Latin in his later "Principles of Philosophy". As Descartes explained it, "we cannot doubt of our existence while we doubt." A fuller version, articulated by Antoine Léonard Thomas, aptly captures Descartes's intent: ("I doubt, therefore I think, therefore I am"). The dictum is also sometimes referred to as the cogito.