"A Letter to Dion" is a philosophical treatise by Bernard Mandeville that was published in 1732. In this book, the author expresses his thoughts on the social and political issues of his time through a collection of letters written to an imaginary friend, the poet Dion. Mandeville uses letters as a form of expression for his ideas about human nature, morality, society and moral values. "Letter to Dion" is distinguished by its deep analysis and acute understanding of the problems of humanity, which makes it a significant contribution to the philosophy of the 18th century.