  We prove the well-posedness of non-autonomous linear evolution equations for
generators $A(t): D(A(t)) \subset X \to X$ whose pairwise commutators are
complex scalars and, in addition, we establish an explicit representation
formula for the evolution. We also prove well-posedness in the more general
case where instead of the $1$-fold commutators only the $p$-fold commutators of
the operators $A(t)$ are complex scalars. All these results are furnished with
rather mild stability and regularity assumptions: indeed, stability in $X$ and
strong continuity conditions are sufficient. Additionally, we improve a
well-posedness result of Kato for group generators $A(t)$ by showing that the
original norm continuity condition can be relaxed to strong continuity.
Applications include Segal field operators and Schr\"odinger operators for
particles in external electric fields.
