Why are the letters I, O, W, X, and Y not used in the Library of Congress Classification?
The Library of Congress Classification (LCC) consists of 21 main classes, each class represented by a letter of the alphabet. Because only 21 classes were required to represent the major subject areas and disciplines classified by the Library, five letters were not included as part of the LCC. The reason that the particular letters I, O, W, X, and Y were not selected for the LCC is a matter of some debate. There are few extant records that document the development of the LCC, and it appears that none which survive discuss why these letters remained unused. Despite the lack of documentation, an oral tradition passed down through generations of Library of Congress catalogers accounts for the exclusion of these letters from the LCC. This tradition holds that the letter I was not used because it is too similar to the number 1; use of an I class would cause confusion for people looking for works which had a call number such as I1, I10, and I111. Similarly, the letter O was not selected beca
