"Philosophy of Praxis"

This is not Capital-related, strictly speaking, although one could certainly say a great deal about why *that* is.

In Gramsci's prison notebooks, most of the proper names of Bolsheviks as well as terms like "Marxism" and "proletariat" are suppressed, so that it is written in a kind of code. "Marxism" therefore becomes "the philosophy of praxis." Now, this is reasonable enough, and after a while you don't really notice, and just read (or translate in) the intended concept for the euphemism. 

My point is, of course it's *not* a euphemism, and it is almost the key concept of Gramsci that Marxism IS the philosophy of praxis.

This can be thought about in two ways. One is the Leninist sense: why in the Russian Revolution did the Bolsheviks, the most extreme and doctrinaire party, triumph over the more palatable and compromising Mensheviks and social democratic parties? The Bolshevik answer would be that the question is tautological. That is, "correct" doctrine BY DEFINITION aligns itself with the "winning" team of history, the proletariat. To be doctrinaire in a revolutionary situation is irreducibly tactical. 

The second sense is expressed by Rosa Luxembourg: academic debates about socialism are anything *but* academic; socialism is a weapon or tool of the proletariat. To water socialism down "in theory" is a real attack on the working class: "It is their skin which is being brought to market." 

In other words, Marxism does not have a set of aims distinct from the plan for accomplishing them; it does not say "We believe this, but we should settle for this." (i.e. we believe that capitalism is bad, but really we can work within it for improvement and leave it standing).

We should read the cliched criticism of leftist intellectuals backwards then: instead of "that's all well and good in theory, but what about practice," Marxism insists that we ask, "that's all well and good in practice, but what about in theory??

Cf. The German Ideology, Critique of the Gotha Programme, and the final section of the Communist Manifesto for Marx's vicious attacks on compromised versions of socialism.

Which brings us back to Capital, which is not at all a "tactical manual" for revolution. There is a great deal to say about this, and I will say it, in the posts covering the final 2/3 of the book.