This is a semi-facetious term made up by (of course) Michael Nagler to describe the very real phenomenon that a small amount of violence can subvert the nonviolent character of a demonstration or, for that matter, a person’s consciousness. As Nagler states his ‘law:’
NV + V = V.
More seriously, this effect is a serious problem for nonviolent actors today, as witnessed by the disruption by a very small number of ‘Black Block’ anarchists of the large, well-disciplined protestors at the Seattle WTO meetings in 1999, and more recently, as it seems, the few passengers of the Free Gaza flotilla who attacked invading Israeli commandos aboard the Mavi Marmara in May of 2010. In both cases the disruptive element succeeded in capturing the lion’s share of media attention and thus changing the character of the event in the eyes of much of the public. The ‘law’ identifies something deeper than just media attention, however: as with other aspects of active nonviolence and Satyagraha, they are like a conversation with opponents, and mixed messages can badly disrupt communication, especially the mixing of, as we say, even a little violence with an otherwise nonviolent movement or event.