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PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
MALINVAUD 
Since we apparently have some time this afternoon, I may 
perhaps be permited to come back on the motivations for my own 
paper. 
Professor KooPMANS has indicated this morning that one of the 
reasons for his own research was to explore the consequences of 
assuming a particular kind of utility for choices over time. This 
was certainly also a part of my own motivations. But I was still 
more strongly motivated by the need to see clearly what we should 
do when we use models with several periods, as a guide for plan- 
ning or programming. 
We can certainly do some programming by considering timeless 
models, Such models proved useful in various countries, in India 
for instance. But multiperiod models are necessary for many que- 
stions: the choice of investments, the discussion of public policies 
nfluencing the saving ratio, even the study of consequences that 
would follow a progressive reduction of the length of work. 
In the multiperiod models now used by programming, terminal 
conditions are imposed. For instance, the future up to 1970 is 
divided into three periods and the capital structure to be in place 
at the end of 1970 is fixed a priori. Since such terminal conditions 
are, to some extent, arbitrary, one may have serious doubts on the 
adequacy of the procedure. 
My research should be considered as an attempt to explore fully 
the nature of the solution in a much simplified model in order to 
understand better the implications of assuming arbitrary terminal 
conditions, and perhaps also to find new ways of dealing with the 
difficulty. All this is done for a one commodity world, but should 
give us some useful insights on what is likely to occur in more disag- 
gregated models. 
DORFMAN 
Are you disagreeing with me: 
[9] Morishima - pag. 38