The Kirkwood Superposition Approximation, Revisited and reexamined

Abstract

The Kirkwood superposition approximation (KSA) was originally suggested to obtain a closure to an integral equation for the pair correlation function. It states that the potential of mean force of say, three particles may be approximated by sum of potential of mean forces of pairs of particles. Nowadays, this approximation is widely used, explicitly or implicitly, in many fields unrelated to the problem for which it was suggested.
It is argued that the KSA is neither a good approximation nor a bad approximation; it is simply not an approximation at all.