Quincas Borba, or 'Philosopher or Dog?', is a profound and satirical novel by the Brazilian master Joaquim Maria Machado de Assis. This philosophical work, a spiritual sequel to 'The Posthumous Memoirs of Brás Cubas', follows the naive schoolteacher Rubião. He inherits a significant fortune from the eccentric philosopher Quincas Borba, along with his dog, also named Quincas Borba, under the condition that he cares for the pet. The narrative intricately explores Rubião's descent into madness, driven by his newfound wealth and the philosopher's bizarre and self-serving 'Humanitism' philosophy. Machado de Assis expertly dissects themes of greed, love, social ambition, and the inherent irrationality of human nature in 19th-century Rio de Janeiro. It's a masterful critique of society and the human condition.