Fuentes is a novelist with a pronounced philosophic bent. In his earlier works he uses the ideas of the existentialist philosophers, especially the French ones. In The Campaign his characters embrace the ideas of the eighteenth-century philosophers, Rousseau, Voltaire, and Diderot. Baltasar Bustos is a follower of Rousseau, Xavier Dorrego finds Voltaire more suitable to his temperament, and Manuel Varela believes that the philosophy of Denis Diderot is a better guide for life and politics. They are close friends who believe that liberty from the domination of Spain is inevitable, but Bustos alone actually fights to achieve this end.

Bustos' quest is a blend of idealism and the passion he feels for a married woman whom he hopes to impress. He has spied on Ofelia Salamanca in her boudoir while plotting to kidnap her child and replace it with the baby of a black prostitute. Ofelia, the wife of the Spanish Viceroy, is not even aware of his existence. Accidentally starting a fire as he leaves her residence, he feels that he probably killed her child and pursues her across revolutionary Latin America to express his regrets. This quixotic purpose is not realized until the end of the novel, and he never learns the full extent of the ironies involved in it.

Varela is the narrator and the ideas of Diderot are the ones which prevail in the story. In his recent writings Fuentes has accepted Diderot's ideas which anticipated the uncertainty principle of a more recent thinker, Werner Heisenberg. Since everything is constantly changing and it is impossible to get a total view of reality anyway, no philosophy can be adequate. Accordingly, history cannot be completely understood either. Baltasar Bustos' quest is futile, then, as all quests must be.

Fuentes has written at length on the importance of Don Quixote in modern literature. An understanding of this novel is for him the test as to whether a reader can ever be an adequate critic. As long as there are men like Baltasar Bustos who will embark on quests despite how ridiculous they may seem to the more practical minds around them, there is hope for the human race.

Fuentes' outlook is not totally pessimistic. Fuentes, who has been something of an ideologue himself, demonstrates in this book that ideologies always impose a kind of blindness when applied in their purest form. European theories were applicable to the conditions of Latin America only to a limited extent. Baltasar Bustos believes that if ideals are passionately pursued, they can be realized. Rousseau has taught him this. His passion is fueled by an ideal erotic passion. In him political goals and private lusts combine. A young bookish philosopher is forced to cope with realities which Jean Jacques Rousseau could not possibly have known.