The Hilbert space approach to the internal (isoelectronic) hardness and softness kernels is presented at the global and subsystem resolutions. A separation of components due to the intramolecular polarization (P) and external charge transfer (CT) is performed by projections into the complementary subspaces spanned by the P-vectors. eigenvectors of the molecular linear response operator. and the constant CT-vector. The quantities reflecting the P-CT coupling are discussed and explicit transformations between the (P,CT)-resolved perturbations and responses are reported. (C) 2002 Published by Elsevier Science B.V.