The separate streams of problems, policies, and politics come together at certain
critical times. Solutions become joined to problems, and both of them are
joined to favorable political forces. This coupling is most likely when a policy
window-an opportunity to push pet proposals or one's conceptions of problems-
is open.
Policy windows are opened either by the appearance of compelling problems
or by happenings in the political stream. Hence, there are "problems windows"
and "political windows." To return to our distinction between the agenda and
the alternatives, the governmental agenda is set in the problems or political
streams, and the alternatives are generated in the policy stream.
One key coupling is that of a policy alternative to something else. Entrepreneurs
who advocate their pet alternatives are responsible for this coupling.
They keep their proposal ready, waiting for one of two things: a problem that
might float by to which they can attach their solution, or a development in the
political stream, such as a change of administration, that provides a receptive
climate for their proposal. Some windows open largely on a schedule; others
are quite unpredictable. But a window closes quickly. Opportunities come, but
they also pass. If a chance is missed, another must be awaited.
While the governmental agenda is set by events in either the problems or political
streams, setting of decision agendas emphasizes, in addition, an available
alternative. A worked-out, viable proposal, available in the policy stream,
enhances the odds that a problem will rise on a decision agenda. In other
words, the probability of an item rising on a decision agenda is dramatically increased
if all three elements-problem, proposal, and political receptivity-are
coupled in a single package.
Finally. success in one area increases the probability of success in adjacent
areas. Events spill over into adjacent areas because politicians find there is a
reward for riding the same horse that brought benefit before, because the winning
coalition can be transferred to new issues, and because one can argue from
precedent.