  We investigate instabilities and their regularization in theories of
gravitation. Instabilities can be beneficial since their growth often leads to
prominent observable signatures which makes them especially relevant to
relatively low signal-to-noise ratio measurements such as gravitational wave
detections. An indefinitely growing instability usually renders a theory
unphysical, hence a desirable instability should also come with underlying
physical machinery that stops the growth at finite values, i.e. regularization
mechanisms. The prototypical gravity theory that presents such an instability
is the spontaneous scalarization phenomena of scalar-tensor theories, which
feature a tachyonic instability. We identify the regularization mechanisms in
this theory, and show that they can be utilized to regularize other
instabilities as well. Namely, we present theories where spontaneous growth is
triggered by a ghost rather than a tachyon, and numerically calculate
stationary solutions of scalarized neutron stars in these theories. We
speculate on the possibility of regularizing known divergent instabilities in
certain gravity theories using our findings, and discuss alternative theories
of gravitation where regularized instabilities may be present. Even though we
study many specific examples, our main point is the recognition of regularized
instabilities as a common theme and unifying mechanism in a vast array of
gravity theories.
