Often, the time derivative in the Faraday–Maxwell equation motivates calling this equation "dynamical", which is somewhat misleading in the sense of the preceding analysis. This is rather an artifact of breaking relativistic covariance by choosing a preferred time direction. To have physical degrees of freedom propagated by these field equations, one must include a kinetic term F ⋆ F for A, and take into account the non-physical degrees of freedom that can be removed by gauge transformation A ↦ A − d α. See also gauge fixing and Faddeev–Popov ghosts.