An extension of Kato's stability condition for nonautonomous Cauchy problem
s is presented. It is proved that in the commutative case this condition an
d a mild regularity assumption imply wellposedness. If one supposes the Kat
o-stability, then the solutions are given by an integral formula. By means
of examples we show that in general these stability conditions cannot be om
itted in our results. Moreover, it is seen that the Kato-stability is not n
ecessary for wellposedness.