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it may be useful to face explictly a spontaneous question which
might be raised at this point. Why should the subject of eco-
nomic growth be approached in this way? The theoretical
scheme of the previous pages is, after all, full of simplifications
and rough approximations. Now, why should such simplifi-
cations be made in preference to others? And in particular,
why should such simplifications be made in preference to those
that traditional economics has adopted so far?
This is a relevant question to ask because, as pointed out
already, any model does entail a simplification of reality and
it is of paramount importance to be clear about the criterion
according to which assumptions are made. One is bound to
make immediately some simplifications in the choice of the
variables and of the constants of any economic enquiry. For,
In economics, there are — rigorously speaking — no constants.
All quantities one may be dealing with are, in fact, variable.
But since some quantities are more variable than others, it is
commonly said that one should take as constants those quantities
which vary the least. This clearly is a reasonable criterion to
follow, provided that it is applied consistently. But there has
been difficulties, connected with the development of economic
thought.
In the last hundred years, economists have just happened
to be interested in the static characteristics of an economic
system, or at most in its short-term behaviour. And since in
the short run hardly any quantity can vary substantially, they
have tended to make the distinction between variables and
constants coincide with the distinction between unknowns and
data. Those economic magnitudes that were to be explained
funknowns) have also been taken as variables, and those
magnitudes that were to be accepted as given (data) have also
seen taken as constants.
Obviously, such an association did not matter very much
as long as it was restricted to a short-run analysis. But
when, recently, the attention of economists has shifted .uo dy-
‘Io] Pasinetti - pag. 67
