Forgive me if this seems a rather basic question, but I would like to settle it once and for all. The concept of "ground", "earth" and "common" confuse me a little. I think I have earth right - this is a path that allows dangerous current to be carried away, eg. if a live wire touched the metal case of an appliance, one would get electrocuted upon touching the case, so, the case is connected to an earth wire which allows this current to flow and hence trip a fuse or breaker. Ground and common confuse me far more. I see in many circuit diagrams that the return paths to a battery are often not indicated, just a ground symbol is used. So, is ground just the return path for current to the source, and this path is at 0 V? Wikipedia says, "Many electronic designs feature a single return that acts as a reference for all signals. Power and signal grounds often get connected together, usually through the metal case of the equipment." Does this mean that the metal case of a device is actually the return path for current to the source?? Perhaps an example of where this confuses me might help: In the bipolar voltage divider, there is a reference ground such that 2 terminals are positive wrt ground and 2 terminals are negative wrt ground...in an actual circuit, what would this ground be physically?