 In social science, this has made his approach popular amongst contemporary Marxists — notably Alex Callinicos – who postulate the existence of real social forces and structures which might not always be observable.What is the difference between what something is, and how it "appears"?– e.g., ""sound is the variation of pressure that propagates through matter as a wave""
Perhaps the most important topic the riddle offers is the division between perception of an object and how an object really is.