  Structural-equations models (SEMs) are perhaps the most commonly used
framework for modeling causality. However, as we show, naively extending this
framework to infinitely many variables, which is necessary, for example, to
model dynamical systems, runs into several problems. We introduce GSEMs
(generalized SEMs), a flexible generalization of SEMs that directly specify the
results of interventions, in which (1) systems of differential equations can be
represented in a natural and intuitive manner, (2) certain natural situations,
which cannot be represented by SEMs at all, can be represented easily, (3) the
definition of actual causality in SEMs carries over essentially without change.
