Caption: Bertrand Russell (1872--1970), mathematician, philosopher when relatively young man.
See also St. Andrews History of Mathematic Archive: Bertrand Russell.
One of Bertrand Russell's points, when he was waxing philosophical---that impressed yours truly as a young person on a long car trip---was that super-pedantically, you could say there are almost NO real direct observations---nothing is directly knowable (or "observed"), except that "there is thinking"---which was probably noted by others too.
Rene Descartes (1596--1650) assumed too much with cogito ergo sum---how does one know there is an "I" to think?
Howsoever, St. Augustine (354--430 CE):