Conversations on the Plurality of Worlds

Conversations on the Plurality of Worlds is a work of popular astronomy and philosophy written in the form of a dialogue. It was published anonymously in 1686 and is attributed to the French writer Bernard Le Bovier de Fontenelle. It presents the astronomical theories of Nicolaus Copernicus and René Descartes through conversations between a narrator and a marquise, divided into six evenings and preceded by a preface and a dedication. The book was intended for educated readers without specialist training, especially from aristocratic and fashionable society.

Fontenelle chose French rather than scientific Latin, a decision that helped the work reach a broad public. In the preface he addresses his female readers and suggests that the explanations should be understandable to anyone without scientific training, a point later praised by some modern feminist movements as a recognition of women's capacity for science. The conversations mix the narrator's explanations with everyday examples and with the marquise's questions and objections, which guide the exposition and translate it into the language of elegant conversation.

The content moves from the near to the distant. The first evening introduces the Copernican system: the Earth is not a motionless centre but a planet that turns on its axis and revolves around the Sun. In the second and third evenings, by analogy, the Moon and other planets are suggested as possibly inhabited worlds. The fourth surveys Venus, Mercury, Mars, Jupiter and Saturn, and the fifth interprets the fixed stars as other suns, each with worlds of its own. The sixth, added in 1687, returns to the arguments in light of recent astronomical observations. Many claims are presented as hypotheses, and the author sets reasoning and observation against the authority of tradition, making the book an exercise in critical doubt.

The work was an exceptional success: it went through thirty-three editions during its author's lifetime and was translated into more than ten languages. It helped spread the Copernican system, still not universally accepted in 1686, although the scientific data on which it rested were limited and in part inaccurate even for its time. The Holy See placed it on the Index of Prohibited Books in 1687, without the book having provoked an open theological controversy. Its historical importance lies mainly in turning an astronomical and philosophical debate into an accessible conversation, and in becoming a reference point for scientific dialogue in the eighteenth century.