How to arrive at Lorenz gauge condition? http://en.wikipedia.org/wiki/Lorenz_gauge_condition I know it's used to simplify the 2 partial differential equations of the potentials, but why can we put such a restriction on the potentials? Doesn't that restriction restrict the possible electrical and magnetic fields that can be derived from the potentials? Could I make any arbitrary restriction on the potentials? For example could I say that the laplacian of A (A being the magnetic vector potential) is equal to 0? I asked my teacher and looked in Jackson's book but they just justify it saying "the potentials are arbitrary".