 Already St. Anselm studied the concept of action in a way that must be classified as logical; had he known symbolic logic, he would certainly have made use of it (Henry 1967; Walton 1976). In modern times the subject was introduced by, among others, Alan Ross Anderson, Frederick B. Fitch, Stig Kanger, and Georg Henrik von Wright; Kanger’s work was further developed by his students Ingmar Pörn and Lars Lindahl. The first clearly semantic account was given by Brian F. Chellas (1969). (For a more detailed account, see Segerberg 1992 or the mini-history in Belnap 2001.)