PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28

DIAGRAM .

: Model in its Environment

> Experience

the system would behave if left to itself but also what would be
the problems and results of trying to change it in various respects,
 the model must be readily computable. Model-building
is a scientific activity but I do not think that a usable model
of an economic system can be built by a group of scientists
working in isolation, for the simple reason that, however wellendowed
 the group may be, it cannot possibly know as much
as it needs to know about all aspects of the economy without
the cooperation of many people engaged in a variety of practical
tasks. The model-builders can of course build a prototype, but
they will be very unwise if they do not seek a great deal of
practical advice before they go fully into production.
The combination of a model with a set of objectives gives
rise to a policy. This is where the politician comes in: he formulates
 the objectives. He may specify objectives in detail or
he may delegate his responsibility, as when, with whatever safe-1]

 Stone - pag. 4