  Experiments reveal that the superconductors $\text{UPt}_3$,
$\text{U}_{1-x}\text{Th}_x\text{Be}_{13}$ and $\text{PrOs}_4\text{Sb}_{12}$
undergo two superconducting transitions in the absence of an applied magnetic
field. The prevalence of these multiple transitions suggests a common
underlying mechanism. A natural candidate theory which accounts for these two
transitions is the existence of a small symmetry breaking field, however such a
field has not been observed in $\text{PrOs}_4\text{Sb}_{12}$ or
$\text{U}_{1-x}\text{Th}_x\text{Be}_{13}$ and has been called into question for
$\text{UPt}_3$. Motivated by arguments originally developed for superfluid
$^3\text{He}$ we propose that a generalized spin fluctuation feedback effect is
responsible for these two transitions. We first develop a phenomenological
theory for $^3\text{He}$ that couples spin fluctuations to superfluidity, which
correctly predicts that a high temperature broken time-reversal superfluid
$^3\text{He}$ phase can emerge as a consequence. The transition at lower
temperatures into a time-reversal invariant superfluid phase must then be first
order by symmetry arguments. We then apply this phenomenological approach to
the three superconductors $\text{UPt}_3$,
$\text{U}_{1-x}\text{Th}_x\text{Be}_{13}$ and $\text{PrOs}_4\text{Sb}_{12}$
revealing that this naturally leads to a high-temperature time-reversal
invariant nematic superconducting phase, which can be followed by a second
order phase transition into a broken time-reversal symmetry phase, as observed.
