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PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - Z( 
lysis which can be carried out for a socialist country as well as for 
a capitalist country. On the other hand, for example, the processes 
through which prices are actually reached are specific to particular 
institutional set-ups: ‘they are different according to whether we 
consider a socialist economy, a capitalist economy, or any mixed 
type of economy. It seems to me that this distinction is preliminary 
to, and should be put behind the classification which have been put 
on the blackboard by Prof. WoLp completed by Prof. Friscx. 
ALLAIS 
I would simply like to make a few remarks on the points which 
have been raised during the discussion. 
In the first place, the thinkers of earlier times do not appear to 
have been as preoccupied with method as in our day. I think that 
this difference results from the unequal development of our science. 
Three centuries ago, at a time when mathematics and physics were 
still only stuttering, DESCARTES felt it necessary to study method. If 
today we economists speak of method, it is simply because our 
science has not yet reached a sufficiently high degree of attainment. 
A second remark: I am struck by the fact that several speakers 
have paid great attention to the question of aims in the construction 
of models. Personally, I feel that models ought to be neutral, and 
constructed independently of objectives. I would willingly associate 
myself with Professor FRISCH’s suggestion that explanatory, fore- 
casting, and decisional models should be distinguished. It is not 
possible to bring science back to a single type of model. Personally 
I consider the most significant type of model to be the explanatory 
one, and I believe that to subordinate the construction of explanatory 
models to the pursuit of certain objectives is potentially very dan- 
gerous. 
A third point is that Professor Koopmans has just said that there 
is a social process of selection, which he described as being very 
useful, and fruitfull both in ideas and in terminology. On the con- 
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