  The microlensing monitoring programs have studied large numbers of standard
light curves which seem to be due to lensing by a dark point mass. Theory
predicts that many microlensing events should display significant deviations
from the standard form. Lens binarity in particular is expected to be common.
So far, however, only a handful of light curves exhibit evidence that the lens
is a binary; all of these display dramatic deviations from the standard light
curve, exhibiting pronounced multiple peaks and/or caustic crossings.
Binary-lens events in which the light curve is less dramatically perturbed
should also exist in the data set. Why, then, have we not detected them? The
answer may lie in the fact that the perturbations, though often significant,
tend to be less distinctive than those associated with caustic crossings.
  We present a method to determine whether a light curve is due to lensing by a
binary. The method works for both gently and dramatically perturbed binary-lens
light curves. Our method identifies all degenerate solutions-- i.e., all
possible lensing events that might have given rise to the observed light curve.
It also enables us to eliminate from consideration large ranges of possible
false positive identifications associated with light curves that might mimic
microlensing by a binary. This method, or a generalization of it, can also be
applied to the analysis of light curves that deviate from the standard
point-mass lens form because of astronomical effects other than lens binarity.
