Models of impact oscillators using an instantaneous impact law are by
their very nature discontinuous. These discontinuities give rise to bi
furcations which cannot be classified using the usual tools of bifurca
tion analysis. However, we present numerical evidence which suggests t
hat these discontinuous bifurcations are just the limits (in some sens
e) of standard bifurcations of smooth dynamical systems as the impact
is hardened. Finally we show how one dimensional maps of the interval
with essentially similar characteristics can exhibit the same kinds of
bifurcational behaviour, and how these bifurcations are related to st
andard bifurcations.