Descartes insisted that everything is self-evident. He also mentioned in passing that he was amazed when he considered how weak his mind was and how prone to error. Therefore he could not be sure that everything is self-evident. Was he deceiving himself? He was probably wise to say that it is only prudent never to place complete confidence in that by which we have even once been deceived. Sadly he died on February 11, 1650 so we can’t be sure he would agree with what is written above.