So maybe he did say it, Descartes I mean, "cogito ergo sum." Or in French, "je pense, donc je suis."
Further research has turned up new possibilities. I let the prof know. I'm helpful that way. Last year, in the Religious Studies class I was taking, the prof decided to explain BC/BCE and AD/CE.
He began by saying, "Who knows what happened in the year 0?"
I said, "There was no year 0."