AA describes alcoholism as an illness that involves a physical allergy[110]:28 (where "allergy" has a different meaning than that used in modern medicine.[111]) and a mental obsession.[110]:23[112] The doctor and addiction specialist Dr. William D. Silkworth M.D. writes on behalf of AA that "Alcoholics suffer from a "(physical) craving beyond mental control".[110]:XXVI A 1960 study by E. Morton Jellinek is considered the foundation of the modern disease theory of alcoholism.[113] Jellinek's definition restricted the use of the word alcoholism to those showing a particular natural history. The modern medical definition of alcoholism has been revised numerous times since then. The American Medical Association uses the word alcoholism to refer to a particular chronic primary disease.[114]