Rosa Luxemburg maintained that the capitalist system can keep up its rate of investment (and therefore its profits) only so long as it is expanding geographically.

The fundamental differences between Marxian and traditional orthodox economics are, first, that the orthodox economists accept the capitalist system as part of the eternal order of Nature, while Marx regards it as a passing phase in the transition from the feudal economy of the past to the socialist economy of the future.

The first essential for economists ... is to ... combat, not foster, the ideology which pretends that values which can be measured in terms of money are the only ones that ought to count.

The misery of being exploited by capitalists is nothing compared to the misery of not being exploited at all.

economics limps along with one foot in untested hypotheses and the other in untestable slogans.

The very nature of economics is rooted in nationalism. ... It [was] developed ... in the hope of throwing light upon questions of policy. But policy means nothing unless there is an authority to carry it out, and authorities are national.

science progresses by trial and error, and when it is forbidden to admit error there can be no progress.