The phrase “I think, therefore I am” means that thinking is the one thing that cannot be faked. It is the one way that individuals know they exist.
This phrase is an English translation of the Latin phrase “Cogito ergo sum.” It was first used by philosopher Rene Descartes. Descartes struggled with a problem that is now called “the problem of knowing,” and sometimes referred to as the “brain in a vat” dilemma. The idea is that the brain is easy to fool. The only way a person knows what he experiences of reality is the truth is by trusting in the sensory inputs of his own brain.
Descartes wondered how people knew their perceptions of reality were not the illusions of a demon. In fact, he went on to ponder how people know whether they exist at all. He mused that his own perception of himself might be an illusion. The answer Descartes came up with for this dilemma was, “I think, therefore I am,” which means that thinking is the one thing he knew could not be artificed. Even if thinking comes from a different place than what is expected, the thoughts still come from the individual and define the individual as real, regardless of any other factors.