  We study the non-relativistic response of a 'diquark' bound by confining
forces, for which perturbation theory in the interaction fails. As
non-perturbative alternatives we consider the Gersch-Rodriguez-Smith theory and
a summation method. We show that, contrary to the case of singular repulsive
forces, the GRS theory can generally be applied to confined systems. When
expressed in the GRS-West kinematic variable y, the response has a standard
asymptotic limit and calculable dominant corrections of orders 1/q,1/q. That
theory therefore clearly demonstrates how constituents, confined before and
after the absorption of the transferred momentum and energy, behave as
asymptotically free particles. We compare the GRS results with those for a
summation method for harmonic and square well confinement and also discuss the
convergence of the GRS series for the response in powers of 1/q.
