  We resolve a seeming paradox arising from a common misinterpretation of
Ben-Naim's theorem, which rests on a pairwise decomposition of the Hamiltonian
of a molecular solute/solvent system into pairwise solute-solvent and
solvent-solvent interactions. According to this theorem, also the solvation
entropy can be decomposed into a solute-solute term and a remaining term that
is -- perhaps misleadingly -- referred to as "solvent reorganization entropy".
Crucially, the latter equals the average solvent-solvent interaction energy,
such that these two solvent-solvent terms do not change the total solvation
free energy. This analytical result has often been used to argue that the
reorganization of the solvent cannot play a role in the solvation process, and
thus to rule out "iceberg"-type solvent shell ordering as a solvation driving
force. However, recent calculations based on atomistic simulations of a
solvated globular protein and spatially resolved mutual information expansions
revealed substantial contributions of many-body solvent correlations to the
solvation free energy. Here we resolved this seeming contradiction and
illustrate by two examples -- a simple Ising model and a solvated Lennard-Jones
particle -- that the solvent reorganization entropy and the actual entropy
contribution arising from many-body solvent correlations differ both
conceptually and numerically. Whereas the solvent reorganization entropy in
fact arises from both solvent-solvent as well as solute-solvent interactions
and thus fails to describe what the name suggests, the mutual information
expansion permits a straightforward interpretation in terms of the entropy
contribution of solvent-solvent correlations to the solvation free energy.
