Yes, it is possible to add a third switch to control two lights. If you add a third switch to a circuit with two lights, it will introduce an additional control point for turning the lights on or off.
Assuming a basic setup where the two lights are connected in parallel, here's what would happen with the addition of a third switch:
When all switches are in the "on" position: Both lights will turn on. This is because the switches are connected in parallel, meaning that when any switch is closed (on position), the current can flow to both lights simultaneously.
If any one of the switches is in the "off" position while the other two switches are in the "on" position: Both lights will remain on. In a parallel circuit, if one switch is open (off position), the current can still flow through the other switches that are closed (on position), allowing the lights to remain lit.
If all switches are in the "off" position: Both lights will turn off. When all switches in a parallel circuit are open (off position), the circuit is interrupted, and no current can flow to the lights.
In summary, the addition of a third switch in a parallel circuit with two lights provides an additional control point, allowing you to turn the lights on or off from multiple locations.