SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 605 
CHAPTER III 
THE SIMPLEST CASE OF ECONOMIC EXPANSION 
POPULATION GROWTH WITH CONSTANT RETURNS TO SCALE 
… À simble dvnamic model 
Our inquiry will now venture into what happens after the 
single period so far considered has elapsed, and into what 
happens in general as time goes by. From an analytical point 
of view, there are two notions of time which may be adopted. 
Time may be conceived of as a succession of finite periods, 
with the supposition that changes take place only between one 
period and the other. Or, time may be conceived of as bringing 
along changes in a continuous way, so that the finite periods 
of the previous procedure become so short as to be infinitesimal. 
For our purposes, it is irrelevant whether the first or the second 
procedure is adopted. But since the second procedure makes 
things simpler, from our point of view, it will normally be 
followed all through the following dynamic analysis. However, 
the arguments will also be re-cast now and then in terms of 
the first procedure, when that appears useful and illuminating. 
If we look beyond the single period of time, all quantities 
considered so far must be dated. The previous short-run model 
remains valid within each period, but from one period to 
another those quantities which have hitherto been taken as 
given (population, technical knowledge, consumption patterns, 
capital stocks) may undergo important changes. 
10] Pasinetti - pag. 35