They are two Latin words: the personal pronoun of 1st person ego ( I ) and the 1st person singular of the present indicative form of the verb sum is esse I was ( to be, to be, to have ) therefore means I am or I am, unless it has wanted to write ergo sum, as in the famous phrase of Descartes: cogito, ergo sum, in which case ergo is an interpreting conjunction meaning then, consequently Therefore, so: I think, therefore I exist, that Descartes said after his methodical doubt.
