  Models of axion inflation based on a single cosine potential require the
axion decay constant $f$ to be super-Planckian in size. However, $f > M_{Pl}$
is disfavored by the Weak Gravity Conjecture (WGC). It is then pertinent to ask
if one can construct axion inflation models in conformity with WGC. In this
work we assume that WGC holds for the microscopic Lagrangian so that $f <
M_{Pl}$. However, inflation is controlled by an effective Lagrangian much below
the Planck scale where the inflaton is an effective axionic field associated
with an effective decay constant $f_e$ which could be very different from $f$.
In this work we propose a Coherent Enhancement Mechanism (CEM) for slow roll
inflation controlled by flat potentials which can produce $f_e \gg M_{Pl}$
while $f < M_{Pl}$. In the analysis we consider a landscape of chiral fields
charged under a $U\left(1\right)$ global shift symmetry and consider breaking
of the $U\left(1\right)$ symmetry by instanton type symmetry breaking terms. In
the broken phase there is one light pseudo-Nambu-Goldstone-Boson (pNGB) which
acts as the inflaton. We show that with an appropriate choice of symmetry
breaking terms the inflaton potential is a superposition of many cosines and
the condition that they produce a flat potential allows one to enhance $f_e$ so
that $f_e / M_{Pl} \gg 1$. We discuss the utility of this mechanism for a
variety of inflaton models originating in supersymmetry and supergravity. The
Coherent Enhancement Mechanism allows one to reduce an inflation model with an
arbitrary potential to an effective model of natural inflation, i.e. with a
single cosine, by expanding the potential near a field point where horizon exit
occurs, and matching the expansion coefficients to those of natural inflation.
