Even in *logical* terms I find your reasoning difficult to follow. If the
profit rate is a "given" in the theory, we can interpret it as a sort of
logical premise. But, as I pointed out in an earlier post, the fact that in
your interpretation the advanced constant capital (an element of that
premise) is given only at the end of the circuit, what we have is that that
*premise* is modified for the *conclusion* of the reasoning. In other
words, I cannot attach any possible concrete meaning to your description of
the profit rate as a "given" even in logical terms.
An additional, more wider complication, is that in what sense can we speak
about a *pure* "logical determination" in Marx's theory. I think its
broadly accepted that his "logic" is one attempting to comprehend the
*historical movement* of capitalist phenomena, i.e. it would be some sort
of "historical logic" or "logic of history". Therefore, it's difficult to
understand how can we exclude the *temporal* nature of *history*, reducing
the processes he describes (e.g. the calculation of profit rate) to an
atemporal vacumm in which past and present are indistinguishable.
Abrazos,
Alejandro