To me, the first question is what Marx himself said about the
valuation of constant capital in his theory, both the flow of
constant capital as one component of the price of commodities
and the stock of constant capital as the denominator in the rate
of profit. Andrew has argued that, in Marx's theory of the
falling rate of profit, constant capital is valued at historical
costs (i.e. not revalued in the case of technological change).
I haved argued that I know of not a single passage in which
Marx said that, in the case of technological change (which is
what the falling rate of profit is all about), constant capital is
valued at historical costs. On the other hand, I know of many
passages (including especially his discussion of the "cheapening
of the elements of constant capital" as a "countertendency" to
the falling rate of profit) in which Marx said that, in the case of
technological change, constant capital is revalued in current
costs. That is why I cannot accept Andrew's interpretation that
Marx valued constant capital at historical costs.
I am not arguing that the valuation of constant capital in
historical costs is necessarily wrong as a statement about the
world. That is a separate question. But I am arguing that the
valuation of constant capital at historical costs is a wrong
interpretation of Marx's theory.
As I have said before, I am still undecided and thinking about:
(1) whether "current costs" for Marx meant costs at the
beginning of the current period or the end of the current
period and (2) whether Marx subtracted the capital loss that
results from the devaluation of constant capital from surplus-
value, the numerator in the rate of profit.
I hope this helps.
Comradely,
Fred