I think it's the passage I quoted a few months ago, here:
> Michael Perelman wrote:
>
>> That is not what Marx wrote. He said that there was a TENDENCY to
>> fall & gave offsetting tendencies. Besides, later scholarship showed
>> that Engels pushed the tendency harder than Marx did in the notes
>> that made up Vols. 2 & 3.
>>
>>
>>
>>
>
> I don't get this. I'm no Marxologist, but you're making it sound as if
> Marx's theory could be summarized as "some things make profits go up,
> other things make profits go down." If that were actually the theory,
> who in hell would care? It would never have become one of the most
> talked-about theories about capitalism in history if that's what it
> were about.
>
> In the Grundrisse, Marx says this about the law of FROP (and he does
> call it a "law," not a "tendency"):
>
>> This is in every respect the most important law of modern political
>> economy, and the most essential for understanding the most difficult
>> relations.
>
>
> A few sentences later, he explains:
>
>> The growing incompatibility between the productive development of
>> society and its hitherto existing relations of production expresses
>> itself in bitter contradictions, crises, spasms. The violent
>> destruction of capital not by relations external to it, but rather as
>> a condition of its self- preservation, is the most striking form in
>> which advice is given it to be gone and to give room to a higher
>> state of social production.
>
> This doesn't sound like an innocuous proposition about why sometimes
> profits rise and sometimes they fall. It heralds the end.
>
> Seth