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tions of the model. For example, having fixed the terminal 
conditions at the end of the transitional period, we may agree 
to choose a path through that period by maximising consump- 
tion subject to the terminal conditions and, of course, to the 
operating conditions of the period itself. For any given set 
of conditions we can use the model to work out a path. If the 
path is unacceptable we must reconsider the conditions that de- 
termined it. 
Or again, the model-builder may require some numerical 
data from the policy maker. For example, he will need to 
know how much is to be spent on public health, education, 
roads and other items of government consumption or invest- 
ment in social capital. He will also need to know the input 
structure of these expenditures. Since all demands on resources 
-ompete with each other, it will be possible to settle priorities, 
including the level of total private consumption, only when 
he implications of these proposed demands have been work- 
>d out. 
ft will be noticed at this point that there is a need for a 
aumber of government sub-models just like the industry sub- 
models advocated earlier. The operation of a health service 
or a defence system is a complicated matter which cannot be 
built into a general model. What is required is a separate 
sub-model for each of these activities. Given an amount of 
money to spend and a set of prices, each sub-model would be 
used to decide how this money should be spent. From this a 
cost structure would emerge for use in the general model. The 
general model might show that some revision in the sums to 
be spent would be necessary. As in the case of industry, there 
would have to be iteration between the model and the sub- 
models. Social cost-benefit analysis should prove of great value 
in this field of research [14] [15]. 
To sum up, the main features of policy-making for a system 
are, in my opinion, as follows. First, the different objectives 
of policy should, as far as possible, be considered together. 
r_ = 
Stone - pag. 27