"The actual fact is that – apart for one or two independent contributions which mark a theoretician advance – since the publication of the last volume of Capital and of the last of Engels’s writings there have appeared nothing more than a few excellent popularizations and expositions of Marxist theory. The substance of that theory remains just where the two founders of scientific socialism left it."
"The scrupulous endeavor to keep “within the bounds of Marxism” may at times have been just as disastrous to the integrity of the thought process as has been the other extreme – the complete repudiation of the Marxist outlook, and the determination to manifest “independence of thought” at all hazards."
"...it is only where economic matters are concerned that we are entitled to speak of a more or less completely elaborated body of doctrines bequeathed us by Marx. The most valuable of all his teachings, the materialist-dialectical conception of history, presents itself to us as nothing more than a method of investigation, as a few inspired leading thoughts, which offer us glimpses into the entirely new world, which open us to endless perspectives of independent activity, which wing our spirit for bold flights into unexplored regions."
"...the theory of historical materialism remains as unelaborated and sketchy as was when first formulated by its creators."
"It is pure illusion to suppose that the working class, in its upward striving, can of its own accord become immeasurably creative in the theoretical domain. ... The active participation of the workers in the march of science is subject to fulfillment of very definite social conditions."
"Only in proportion as our movement progresses, and demands the solution of new practical problems do we dip once more into the treasury of Marx’s thought, in order to extract therefrom and to utilize new fragments of his doctrine. But since our movement, like all the campaigns of practical life, inclines to go on working in old ruts of thought, and to cling to principles after they have ceased to be valid, the theoretical utilization of the Marxist system proceed very slowly."
"If, then, today we detect a stagnation in our movement as far as these theoretical matters are concerned, this is not because the Marxist theory upon which we are nourished is incapable of development or has become out-of-date. On the contrary, it is because we have not yet learned how to make an adequate use of the most important mental weapons which we had taken out of the Marxist arsenal on account of our urgent need for them in the early stages of our struggle."