  The existence of universal soft limits for gauge-theory and gravity
amplitudes has been known for a long time. The properties of the soft limits
have been exploited in numerous ways; in particular for relating an n-point
amplitude to an (n-1)-point amplitude by removing a soft particle. Recently, a
procedure called inverse soft was developed by which "soft" particles can be
systematically added to an amplitude to construct a higher-point amplitude for
generic kinematics. We review this procedure and relate it to
Britto-Cachazo-Feng-Witten recursion. We show that all tree-level amplitudes in
gauge theory and gravity up through seven points can be constructed in this
way, as well as certain classes of NMHV gauge-theory amplitudes with any number
of external legs. This provides us with a systematic procedure for constructing
amplitudes solely from their soft limits.
