Virtual power principle and Maxwell's tensor: which comes first?

Purpose The purpose of this paper is to clarify the status of Maxwell's tensor with respect to the virtual power principle (VPP). Design/methodology/approach Mathematical analysis is employed. Findings The VPP, logically stronger, is more fundamental. Maxwell's tensor derives from it, under further restrictive assumptions, and hence, its range of applicability is limited. In particular, it fails to deal with some aspects of magnetostriction. Originality/value The paper shows that when magnetic constitutive laws depend, locally, on strain, the body force is not, as a rule, the divergence of the Maxwell tensor. People who intend to compute forces this way should be wary of that.