There is a useful, broad classification of scenario exercises: whether they
are a forecast or a backcast. While both procedures have
a similar end product - a future state and a path to reach it - the process
for generating the product is very different.
starts with the current situation and possible future paths,
then deduces an end-state.
starts with the current situation
and an end-state and then deduces possible future paths.
In a backcast, there is usually some judgement about the desirability of the future
state. Because of this, backcasts are sometimes called normative scenarios,
while forecasts are sometimes called descriptive or exploratory