In “Marx’s Ethics,” Popper sets out to evaluate Marx’s views on morality. The author argues that Marxist ethical theory is not identifiable directly. Marx’s criticism of capitalism in its entirety can be qualified as a moral condemnation, as he perceived it as slavery (403-05). However, at no point does Marx present ethical ideals as such despite the fact that Capital is a “treatise on social ethics” (405).

Next, Popper emphasizes the significant impact that Marx had on Christianity because of its moral appeal (416). He credits him with the decline of Christian movements that endorsed capitalist exploitation, especially on the European continent. The author even likens Marx’s influence on Christianity to that of Luther on the Roman Catholic Church (406).

Marx was also a forefather of what is called activism today. He argued that people must prove themselves in actions, not words (407). For Marx, socialism is the “kingdom of freedom” in which man is a “master of his own environment” (407). However, Popper contrasts this call to action with Marx’s pervasive historicism, including his belief in the “inexorable laws” of history and the “natural phases of its evolution” (407), which undermine activism.