It is shown that breakdown of insulating or dielectric material may be caused either by polarizable particles or permanent dipoles. Induced dipoles as well as permanent dipoles may gather at a place of maximum stress and form a bridge. Bridges consisting of permanent dipoles may cause the gap between the valence energy band and the conduction energy band to be filled by impurity or imperfection levels. The low ionization potentials of electrons attached to permanent dipoles may facilitate breakdown. An attempt is made to reconcile Crowe’s results with ours.