In “The Aftermath,” Popper discusses the sources of our knowledge, biases, and ideologies and advocates for democratic institutions as guarantors of freedom of thought and progress (429). Our thoughts are part of the greater social environment. This environment is responsible for the thinker’s opinions even if those opinions seem naturally occurring (420). The system of assumptions in its entirety is referred to as “total ideology” (420). Sociology of knowledge is a subject area focused on identifying and analyzing the way that knowledge and reason are linked to society (421, 431). Along with Kant, Popper subscribes to the “activist theory of knowledge” (421), rather than “the receptacle theory of knowledge” (420). Knowledge is not a gift but the logical consequence of one’s own mental labor.

The notion that opinions are determined by class interest advocated by Marx is in line with the sociology of knowledge (429). Popper considers the tension between the rational and the irrational to be one of the key problems of the 20th century with roots in ancient Greece (429, 434). He defines rationalism as an acceptance of opposing arguments and learning from them—this is Socratic rationalism (431, 433). Indeed, every human can serve as the source of learning and deserves to be heard (431, 442).