4 ideas
After a night spent lamenting the injustices of 1770s Paris, the narrator falls asleep and wakes as an old man in the year 2440. A guide shows him a reformed city: the Bastille demolished, orderly streets, simple dress, reformed hospitals, no crushing taxes, and a deist civic religion. The tour ends at the ruins of Versailles, where he is bitten by a snake and wakes back in his own century.
Earlier utopias sit on remote islands, so the ideal society is somewhere else and unreachable. Setting it in the future of a real city makes utopia a destination the present can reach through gradual reform. This turns social criticism into an implied program and a forecast of progress.
In 2440 the vast royal library has shrunk to a small cabinet, because the citizens burned books they judged frivolous, false or morally harmful and kept only condensed essentials. Mercier presents this as improvement. On this view, enlightenment advances by subtracting clutter and error, not by piling up texts.
The book shows current institutions such as the Bastille, Versailles, monasteries and luxury through the eyes of people who have already discarded them. What looks permanent becomes a relic or a ruin. Imagining how a better future will remember the present strips familiar arrangements of their air of necessity.