Observations concerning virtual power

A 'principle of virtual power' has been re-introduced in recent years into the continuum mechanics literature, and used in the modeling of material behavior that involves multiple length scales. In these works, the 'principle' is stated for arbitrary parts of a body and this flexibility is used, to a certain extent, to draw conclusions concerning the structure of the theory that results. However, this arbitrariness, when fully applied, carries many consequences that have been overlooked. Here, a theorem and an example application are given to illustrate the restrictive nature of the 'principle', as it has been stated, and to draw attention to its severe consequences: consequences that question the appropriateness of the conclusions that have been reported in the recent literature.