It is generally argued that Maxwell equations are manifestly Lorentz covariant while the electromagnetic stress–energy tensor follows from the Maxwell equations; thus the EM momentum defined from the EM tensor certainly respects the principle of relativity. This is not exactly true. As indicated by Sheppard and Kemp, "the original debate is in regard to the 4×4 energy-momentum tensor [electromagnetic stress–energy tensor". Minkowski tensor is a real Lorentz four-tensor, apparently leading to Minkowski momentum, although it is non-symmetric. According to Maxwell equations, Abraham constructed symmetric Abraham tensor by assuming that Abraham momentum is correct momentum. However Abraham tensor is not a Lorentz four-tensor at all, although treated as a tensor to get Abraham force, which is seriously contradicting the principle of relativity.