In the course of his study of the sound system of Old Chinese, Karlgren focused on clues provided by phono-semantic compound characters.
His "homorganic principle", asserting that the initials of characters sharing a phonetic component had a common point of articulation, has been central to subsequent studies of Old Chinese.
An extensive revision incorporating the results of Karlgren's studies of pre-Han texts, the Grammata Serica Recensa, appeared in 1957.
n. 字 *dz'i̯əg / dz'i- / tsï to breed (Yi); nurture (Shï); to love, fondle (Shï); to foster (Tso); adolescent's name, designation (Tso); compound character in the script, written character (Han time text ex.).
The names of texts containing the various uses are abbreviated, here Shï for Shijing, Lunyü (The Analects), Tso for Zuo Zhuan, Shu for Shujing and Yi for I Ching.