  We examine the importance of second order corrections to linearized
cosmological perturbation theory in an inflationary background, taken to be a
spatially flat FRW spacetime. The full second order problem is solved in the
sense that we evaluate the effect of the superhorizon second order corrections
on the inhomogeneous and homogeneous modes of the linearized flucuations. These
second order corrections enter in the form of a {\it cumulative} contribution
from {\it all} of their Fourier modes. In order to quantify their physical
significance we study their effective equation of state by looking at the
perturbed energy density and isotropic pressure to second order. We define the
energy density (isotropic pressure) in terms of the (averaged) eigenvalues
associated with timelike (spacelike) eigenvectors of a total stress energy for
the metric and matter fluctuations. Our work suggests that that for many
parameters of slow-roll inflation, the second order contributions to these
energy density and pressures may dominate over the first order effects for the
case of super-Hubble evolution. These results hold in our choice of first and
second order coordinate conditions however we also argue that other
`reasonable` coordinate conditions do not alter the relative importance of the
second order terms. We find that these second order contributions approximately
take the form of a cosmological constant in this coordinate gauge, as found by
others using effective methods.
