The only fact which he does not doubt is the fact that he is thinking, e.g. the well - known Cogito ergo sum (I think therefore I am). (faith.org.uk)
Cristin Tierney Gallery is pleased to announce peter campus: video ergo sum at the Jeu de Paume. (cristintierney.com)
From such a standpoint a more secure foundation for knowledge might instead be, «I am related, therefore I am» (Cognatus ergo sum). (religion-online.org)