PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA 
can be ‘given’ in all its details by a central authority; an 
obvious example of this is the composition of consumers’ expen- 
diture. Another reason is that objectives are multiple and 
conflicting: many of them can be satisfied in several ways 
which have substantial, differential effects on others. Finally, 
it is impossible to state the objectives that make up a policy 
without knowing a great deal about feasibility and cost. In 
each case the necessary knowledge can only come from the kind 
of analysis that a model is designed to provide. 
An important question at this stage is the range of problems 
that the politician would like to see integrated. For example, if 
the model is a national model with no regional dimension, it 
can say nothing about locative problems. If there is to be a 
regional aspect to economic policy, then the model must be 
capable of providing solutions for the different regions. A re- 
gional dimension to an economic model is useful because it 
makes people think why they want particular things to take 
place in particular localities and enables them to compare the 
costs of the alternatives. 
Thus we see that the politician needs the help of the model- 
builder in formulating a policy, just as the model-builder needs 
the help of many other people in building his model. We also 
see that the objectives from which the policy will be shaped get 
into a model in various ways. 
An objective may be built into the model. This is the case 
where it is agreed that private consumers should be left to decide 
how they spend their money. In effect the policy maker says to 
the model-builder: I shall tell you how much money to assume 
available for private spending; your job is to find out how this 
spending will be allocated given the shadow prices that emerge 
from your model, and what indirect demands it will place on 
the system. In the course of drawing up the policy, alternative 
calculations are sure to be needed, but the maximisation of the 
average consumer’s utility forms an integral part of the model. 
Or, an objective may form a constraint on acceptable solu- 
[1] Stone - pag. 20