  The effects of virtual light quark pairs on the charmonium spectrum are
studied. Pair creation is modelled with a ``$^{3}P_{0}$" vertex and
intermediate states are summed up to 2S excitations. Quark model parameters are
obtained by fitting to 12 well-known charmonium states, allowing for feedback
between the decaying particle and the induced mass shifts. Both of these
technical steps are new and improve agreement with the experimental spectrum.
In general, the masses receive small shifts once model parameters are refit.
This is true in almost cases except the $\chi_{cJ}(2P)$ multiplet, which
experiences upwards mass shifts of order 150 MeV, has the ordering of the
multiplet rearranged, and pushes the erstwhile $c\bar{c}$ ${2}^3P_1$ state well
above $D^*\bar{D}$ threshold--observations that clarify the nature of the
enigmatic $X(3872)$
