  We discuss constraints imposed by soft limits for effective field theories
arising from symmetry breaking. In particular, we consider those associated
with anomalous conformal symmetry as well as duality symmetries in
supergravity. We verify these soft theorems for the dilaton effective action
relevant for the a-theorem, as well as the one-loop effective action for N=4
supergravity. Using the universality of leading transcendental coefficients in
the alpha' expansion of string theory amplitudes, we study the matrix elements
of operator R^4 with half maximal supersymmetry. We construct the non-linear
completion of R^4 that satisfies both single and double soft theorems up to
seven points. This supports the existence of duality invariant completion of
R^4.
