Some comments on David's post of 11/24/97.
Hi David,
As always, it's good to hear from you even when we find ourselves
disagreeing.  Since you state that
"I have not been able to follow all aspects of the discussion between 
John and Duncan on this topic, and have not kept copies of all of their 
posts." 
I thought I'd first review some of the points I made in previous posts 
and then comment on yours.
1.  Using Marx's idea of moral depreciation, I was unable to develop
    a way in which the amount of that type of depreciation could be
    seen as part of "c" (used up fixed capital) such that the capital
    value advanced as fixed capital would be preserved as technical 
    change takes place.  I had rejected the idea that moral depreciation
    was simply a deduction from profit.
2.  How to separate depreciation from profit using present values was
    unknown to accountants until several years (about 6 or so) after
    Marx's death.
3. "The Effect of Turnover on the Rate of Profit", the title of Chapter
    4 of Vol. 3 of Capital, was entirely written by Engels as Marx left
    him with nothing but a blank page for that chapter.  There we find
    nothing concerning the depreciation and turnover of fixed capital 
    and its effect on the rate of profit.
4.  Dumenil and Levy note the difference between the RRI and the rate of
    profit in their study of the rate of profit in the U.S.  Concerning the
    RRI, they cite Fisher and McGowan's piece published in 1983 in the 
    AER.  The responses to that article and the rejoinder by Fisher are
    also noted by Dumenil and Levy.     
 
    In that rejoinder Fisher acknowledges his precursors.  One of whom is
    Harcourt (1965) who in turn traces his interest in depreciation to 
    Robinson.  
    
    Basically, Fisher and Harcourt show why the RRI will generally 
    deviate from the accounting rate of profit.  Dumenil and Levy 
    respond to this, not by denying it, but by using data to show that
    the RRI and rate of profit seem to move in the same fashion over
    time.  In their book, however, there is a 10 year lag between the 
    RRI and the rate of profit.  
5.  In a post last summer(?), I noted that by simply assuming that capital
    accumulates with no technical change and a constant RRI, the rate
    of profit can fall (It could also increase depending on the 
    assumptions.) as the stratification of fixed capital changes.  
    Duncan was quick to point out that the "more sophisticated"  studies 
    of the rate of profit took into account this possibility.   Here, 
    as I recall, he noted the works of Dumenil and Levy and that of 
    Robert Gordon.
         
    Dumenil and Levy uncover increasing stratification of fixed capital
    in U.S. economy shortly prior to as well as after the depression.  
    As I recall shortly after the end of WWII, stratification decrease.
    As Duncan told us recently, they are exploring this phenomenon as
    we speak and, according to Duncan, have a paper concerning this
Enough of this, now on to your post.
David wrote:
     The rate of return on investment is essentially the internal rate of 
return to a specific purchase of capital goods, computed by discounting the 
(finite or infinite) stream of future returns and equating the sum of such 
discounted returns to the cost of the capital goods.  As we all learned in 
school, this is formulated as
     K = P1/(1+r) + P2/(1+r)^2 + . . . + Pn/(1+r)^n  (for the finite case)
John comments:
Here, I think we are talking about apples and oranges.  I would write:
     K = A1/(1+r) + A2/(1+r)^2 + . . . + An/(1+r)^n  (for the finite case)
where An=Pn+Cn, Pn is the profit or surplus value, Cn is the amount of
fixed capital used up in period n, given that advances of circulating
capital are assumed to be negligible.   We then have a way of 
computing r, the RRI, in the case of depreciating fixed capital.
What I cannot understand is how your formula tells us anything about
capitalists recovering their initial investment.  Am I missing 
something here or should I give more attention to your concluding 
remark that 
David wrote:
I can't offer any suggestions concerning depreciation.  I have been 
working with "pure fixed capital" models too long!
John comments:
Well, as you might have guessed, I think those "pure fixed capital 
models" can be misleading.
Take care,
John