Its fairly simple: The internal analog switches themselves run off the V+ and V- supplies, and all their pin voltages must *always* be within the rail voltages connected to V+ and V-. Both V+ and V- must be connected. The control logic uses Gnd as its input logic '0' level reference so you need to connect Gnd to the ground(0V) of whatever is controlling it. The control circuit must *NOT* be floating with respect to V+ and V-, and for correct operation, Gnd must be between (V+)-4V and V-.