18 May 15

Bertrand Russell was born on this date in 1872. He is most famous in philosophy and mathematics as the coauthor (with Alfred North Whitehead) of the 1910-1913 books Principia Mathematica, revealing the common foundations between mathematics and formal logic. Counting sheep or money is not simply noticing how many things you have, but is a well-defined operation of applying the same logical principles that govern all reasoning. In other words, arithmetic "works" because it follows exactly the same rules as our definitions for words and our conclusions about causes and effects. (This was exciting news to mathematicians and philosophers in 1910!) Russell was also an ardent atheist, and a pacifist who strongly opposed all nuclear weapons. My "Rodin Thinker" tie is appropriate for this day!