Re: flow or stock?

["Dr. Bruce McFarling" <ecbm@xxxxxxxxxxxxxxxxxxx>]

Harry Veeder <eo200@xxxxxx> wrote,

on Sun, 18 Aug 2002 10:44:18 +0100,
> When we go off to work each morning, what lets us cross the

> street is the presence of the street, not the assumption of
> continuity.

But crossing the street takes time, and without continuity
why would you assume that the street will still be there
when you are halfway across?

And without a weaker assumption of continuity, why even
go to the street on the assumption that it will be there?
Certainly on some days it will not be in a shape for
crossing ... it may be under repair, under water, etc. ...
but we anticipate that it will in all likelihood be THERE,
until we get information to the contrary.  Further, that
anticipation is sufficiently accurate sufficiently
frequently for us to obtain a net benefit from it ...
we are, after all, merely talking about actuarial
reliability, not about precise foreknowledge.

Further, bear in mind that IF the system is non-ergodic,
there is still the possibility of introducing controls
to help steer the system.  In economic models featuring
ergodicity, the assumptions of the model eliminate the
need for many of the institutions which real life
uncertainty motivates us to create.  Indeed, some
useful economic indicators, like building permits, are
useful because of institutions developed to reduce
uncertainty in other area, like whether the builder is
a shonky operator and the building is likely to fall
down shortly after the builder has been paid.