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):

You, who wish to know, do you know you are? I know it. Whence are you? I know NOT. Do you feel yourself single or multiple? I know NOT. Do you feel yourself moved? I know NOT. Do you know that you think? I do.
---St. Augustine (354--430 CE) Quotation from A History of Western Philosophy (1945), p. 355 by Bertrand Russell (1872--1970).

Images:

1. Credit/Permission: Anonymous photographer printed in Bertrand Russell, Justice in War-Time, 1916 / Public domain.
   Image link: Wikipedia: File:Honourable Bertrand Russell.jpg.
   
2. Credit/Permission: © Dutch National Archives, 1957 (uploaded to Wikimedia Commons by User:Alvaro Marques Hijazo, 2018) / CC BY-SA 1.0.
   Image link: Wikimedia Commons: File:Bertrand Russell cropped.jpg.
   
3. Credit/Permission: Anonymous photographer, circa 1960 / Unknown, but it's just hotlinked and its commonly found online.
   Image link: Your thought for today: Alas, now a dead link.