An event or state of affairs dependent on another, uncertain event or occurrence. Contingence is the influence of the history of a system in determining its response to an input (Lane (2001) TIBG 26). In the context of a fluvial system, for example, the response of a length of bank to a hydrological event will be influenced by the bank morphology resulting from a previous event. Hysteresis—the dependence of the equilibrium position of a system on what happens during the process of dynamic adjustment—seems to be the human geographer’s term for contingence (J. Rogers Hollingsworth and R. Boyer, eds. (1997); Vandenberghe and Woo (2002) PPG 26, 4; Jordaan (2005) PHG 29).