  The amplitudes in perturbative open string theory are examined as functions
of the tachyon condensate parameter. The boundary state formalism demonstrates
the decoupling of the open string modes at the non-perturbative minima of the
tachyon potential via a degeneration of open world-sheets and identifies an
independence of the coupling constants $g_s$ and $g_{YM}$ at general values of
the tachyon condensate. The closed sector is generated at the quantum level; it
is also generated at the classical level through the condensation of the
propagating open string modes on the D-brane degrees of freedom.
