My understanding is that a diode conducts current if the voltage at its anode is larger than the voltage at its cathode. I don't understand this. 1) Once the diode begins conducting current, the voltages at the anode and the cathode are identical (the diode serves as an open wire). Therefore, by its own rule, the diode ought to stop conducting current. 2) I heard that the voltage at the anode must be at least 0.7 volts higher than the voltage at the cathode. Is that true, even for an ideal diode? I know the constant 0.7 may differ, but I'm just looking for a general principle.