Morphy Number (mine is 7)

The Morphy number is a measure of how closely a chess player is connected to Paul Morphy (1837–1884) by way of playing chess games.

As of October 2019, there are very few known living players with Morphy number 3. Many ordinary players have a Morphy number of 6 or more.

People who played a chess game with Morphy have a Morphy number of 1. Players who did not play Morphy but played someone with a Morphy number of 1 have a Morphy number of 2. People who played someone with a Morphy number of 2 have a Morphy number of 3, et cetera.

The idea is similar to the Erdős number for mathematicians, the Bacon number for actors, and the Shusaku number, the equivalent for the board game of Go.

Origin

Taylor Kingston states that the idea of the Morphy number may have originated in a June 2000 note by Tim Krabbé, who has Morphy number 4. Krabbé wrote "I once played an official game with Euwe, who played Tarrasch, who played Paulsen, who played Morphy."

Morphy number of famous players

These are players who are important in making links for Morphy numbers.
Morphy number 1

Morphy is known to have played about 100 people, but all of the known links for players with Morphy number 2 go through the following five players. A few years after the early lists of players were tabulated, it was discovered that Mortimer was Morphy's friend and he played casual games with him, so is MN1, so previous lists needed to be drastically revised to promote many players. This is because Mortimer had a very long, if not particularly successful, career, including the Ostende-B 1907 tournament. This enabled many famous younger players to gain MN2. These include Mieses, Tartakower, Znosko-Borovsky, and Bernstein, who played beyond WW2, enabling still younger players to become MN3. Some Irish players could go through the Rev. Dr George Salmon, who played in one of Morphy's blindfold chess simultaneous exhibitions.