Expanding tourism gave landscape paintings a purpose to fill, filling the public's love of the picturesque. 18th century artists defined picturesque as the pleasurable, aesthetic mood that natural landscapes inspired. Romantics, on the other hand, translated landscapes into the mood of the viewer, making landscape paintings a sort of poetry. Nature was used not just as a "pretty picture" but as an allegory for spiritual, moral, historical, or philosophical issues. Artists could "naturalize" conditions, making them seem normal, acceptable, or inevitable. The landscape contributed to the Romantic's idea of nature unified with god and the spirit, so artist may not only depict nature but also participate in it.