The philosophical dialogue, whose definitive model was established by Plato since the golden age of Greek philosophy, fulfills specific philosophical purposes that it achieves thanks to its particular form, and which are different from those of other means of philosophical expression, such as the essay or the treaty. These peculiarities of the philosophical dialogue, as a particularly appropriate means to express rhetorical virtues, made it very popular among Renaissance humanists, who defended the irreducible unity of form and content, against the precepts of Scholasticism, which assumed that the form was a simple inconsequential wrapper for what really mattered, the factual content. Thus, the humanists made philosophical dialogue not only a means to demonstrate their own particular theses, but a demonstration, in itself, of the rhetorical capacity inherent in dialogue to express philosophical nuances unattainable for the rigid discourses of strict rationalism. This article analyzes the specific characteristics of the form of the Philosophical Dialogues of Juan Gines de Sepulveda, one of the most notable humanists of the Spanish Renaissance, and the way he deals with modern issues such as personal ambition of fame and glory, or the relationship between active life and passive life, matters of great interest to pragmatic and civic Humanism.