In lecture four, we learn about realism in Western philosophy through the contrasting views of Plato and Aristotle. We examine Plato’s theory of Forms, where abstract universals like justice or triangularity are the true realities and physical objects are mere shadows, and contrast this with Aristotle’s view that individual substances, like particular humans or horses, constitute reality. The lecture concludes with Aristotle’s analysis of substance, including essential and accidental properties, highlighting how these two approaches offer radically different ways of understanding reality.