The present invention comprises an intuitive algorithm embodiment. In said intuitive algorithm embodiment, a programmable thermostat that operates under control of a control program incorporating an intuitive algorithm. The intuitive algorithm allows a user to change the modes and setpoints of a programmable thermostat without need to refer to a display of currently effective operational modes, setpoints, or environmental sensor inputs. While a user may prefer to observe said display, the intuitive algorithm eliminates the need to do so.