In the 19th century, the ampersand was recognized as the 27th letter of the alphabet, right after «Z,» and taught as such to British schoolchildren. At the time, it was common to refer to letters that could also be interpreted as words as per se letters: e.g. per se «A» (as opposed to article «A»), and per se «I» (as opposed to pronoun «I.») Since it stood for «and,» the ampersand was the third of these per se letters, so when school children recited their ABCs, they ended it: «…W, X, Y, Z, and per se and.» Get a couple generations of kids slurring «and per se and,» and you get the word ampersand. John Brownlee .