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.
As of October 2019[update], there are very few known living players with Morphy number 3. Many ordinary players have a Morphy number of 6 or more.[2]
The idea is similar to the Erdős number for mathematicians, the Bacon number for actors, and the Shusaku number, the equivalent for the board gameofGo.
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."[2][3]
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.[1][4]
A few years after the early lists of Morphy numbers tabulated, it was discovered that a fifth player, James Mortimer, was Morphy's friend and he played casual games with him. This gives Mortimer a Morphy number of 1, creating a need to drastically revise those previous lists to include many more players.[4][5] 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 a Morphy number of 2, including Mieses, Tartakower, Znosko-Borovsky, and Bernstein, who played beyond WW2, enabling still younger players to gain a Morphy number of 3, and so on.
Everyone in this group played someone in the group above. The Australian champion Frederick Esling achieved MN2 by beating Anderssen in an offhand game[6] and another Australian champion, Julius Leigh Jacobsen (1862–1916)[7] achieved MN2 by beating Bird in a casual match +4-2=1, enabling many Australian players of the early 20th century to achieve MN3.[8]
The following are some of the most important players who have achieved MN2.[1]
Most of the masters in this group played several members of the previous group. This group includes some of the most important players for making connections to later generations. Botvinnik and Reshevsky played older masters such as Lasker and Janowski, had long careers, and played many younger players.[1] Najdorf was Tartakower's pupil and they played a number of published games together, and Najdorf played blitz right into his 80s, allowing many younger players to achieve 4. Smyslov and Keres had very long careers, so much younger players achieved MN4 by playing them. Gligoric also played Tartakover,[17] allowing many Yugoslav players to achieve 4. C.J.S. Purdy played Tartakower,[18] enabling many Australian players to achieve 4. Fairhurst, who played Tartakover,[19] was many times champion of Scotland, and later moved to New Zealand, so a number of players in these countries achieved 4 by playing him.
As of 2013[update], many of the top grandmasters were thought to be in this group (along with a large number of lower-rated players).[1] However, several players initially thought to be in this group were actually MN4s;[53] for instance, based on playing Smyslov, who played Tartakower and Bernstein.
^Mortimer played Sir George Thomas in the Canterbury 1903 and Brighton 1904 tournaments. Gino de Felice, Chess Results, 1901-1920, McFarland & Co., 2006, pp. 26, 37.
^Played Eugene Ernest Colman, Morphy number 2, at least three times, 1947-1953; scores recorded in Surviving Changi: E E Colman by Olimpiu G Urcan (Singapore, 2007)
^Robert Wade played Savielly Tartakower twice, in 1951 (Staunton Memorial) and 1953 (Hastings). He also defeated Ossip Bernstein at the IBM Amsterdam tournament in 1961.
