Why is Don Quixote often considered the first modern novel?

Don Quixote is widely regarded by literary historians as the first modern novel because it fundamentally transformed prose fiction through its innovative structure and depth. While earlier works existed, Cervantes’s masterpiece moved beyond the static characterizations of previous genres to establish several key elements of the modern form:123

• Psychological Realism: Unlike the rigid archetypes of chivalric romances, the characters of Don Quixote and Sancho Panza evolve throughout the narrative. Their relationship is dynamic, with their perspectives on reality constantly shifting and influencing one another.42
• Heteroglossia: Cervantes employed what critic Mikhail Bakhtin called heteroglossia, or "multiple voices," by incorporating a diverse array of characters with conflicting beliefs and opinions, which added significant complexity to the narrative.4
• Philosophical Depth: By presenting reality on two levels—the "poetic truth" of the knight and the "historic truth" of his squire—Cervantes used the interaction between these rarely compatible worldviews to provide profound philosophical commentary on human existence.2
• Self-Reflexivity: In Part II, Cervantes demonstrated an awareness of the power of the printed word, as the characters become aware that their own adventures are being read by others, highlighting the cultural impact of literature.4