Justin: This isn't as clearly expressed as it might be, but I didn't intend to suggest that Engels or Lenin were wrong in their theories of knowledge I also didn't intend to suggest that they were right. I just didn't comment on them
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CB: I didn't intend to imply that you suggested that their theories were wrong, rather that I was seeing substantial agreement between yours and theirs.
%%%% Btw, the idea that strictly false theories like Newtonian mechanics may be accepted as good enough for a particular purpose isn't the same as the idea that practice is the test of truth. The latter idea affords a testing procedure: a theory is more likely to be true if accepting it helps you get what you want or attain your aims.
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CB: Yes, I see what you mean. I'd say Newton's theory is relatively true, not strictly false. All interesting theories are "strictly " speaking false, because we don't have absolute truth. Well, that Napoleon is dead is absolutely true.
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That is not exhaustive, because (a) inconsistent theories may do that, (b) you may have other grounds for thinking a theory true or false, and (c) sometimes false theories are more likely to lead to practical success
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CB: You may have mentioned it in the course of this thread and I missed it, but the test of theory other than practice is what ?
You'd have to give an example of inconsistent theories being proven equally valid by practice.
The Engels-Lenin idea is that all true theories are relatively true. That trial and error is critical in the development of relative truths. All theories are also, relatively false , too.
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The pragmatic/Marxian idea that practice is the test of truth is based in the idea that if you track accurately track the way the world is, carve it at the joints, as it were, you are more likely to get what you want. Point (c) raises a problem for Marxism in that light, because Marx's theory of ideology is based on the idea that false theories are more likely to get you want you want in some cases. Thus the bourgeoisie is more likely to stay in power if it obscures the reality of exploitation. Hence neoclassical economics. The question is, then, why isn't historical materialism like that? That is, a false theory more likely to get workers what they want, say, by giving them an unrealistic expectation of success in bringing about socialism that is higher than it would be if they believed the truth?
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CB: Yes, nice argument turning Marxism' epistemology on itself.
One thought I have is that I am not sure the analogy is set up correctly. The objects of study in natural science wouldn't cognize the theory as part of its fulfillment or failure, whereas here, the "objects" as "subjects" can cognize.
I think Marx recognizes a qualitative difference between natural and historical science.
My version of your "paradox" is to say if all Marxist revs have failed , then Marx's theory fails his own test of practice; But I think Marx gives his theory an epochal timeframe, so we might expect we are still within his time "limit".
Of course, I say the Marxist revs so far are/were trials and errors, "relative truths" .