Abstract: The concept of limitation is addressed in this article around the eighteenth-century discussions between materialists and immaterialists. In particular, the article focuses on the theses of the materialist perspective regarding the materiality of the soul and its confining in the natural world, supporting in this sense a monistic view of reality. The authors considered will be La Mettrie for the mechanistic view, and D’Holbach for the criticism of the supernatural world and the idea of «spiritual soul».