There is an overwhelming sense that the modern world that Hemingway shows us runs the risk of drifting dangerously far from the natural world. The author sets up a clear-cut opposition between the decrepit urban space of Paris and the rejuvenating, healthy realm of Nature. Furthermore, many of the characters are divorced not only from capital-N-Nature, but from their own natural states; the perpetual drunkenness and self-imposed oblivion that dominate the book remove characters from their true thoughts and emotions. Our protagonist and a few other characters share a profound appreciation for nature, and in it they are able to take refuge from the negative effects of an unsatisfactory, unhealthy society.
During Bill and Jake’s fishing trip, their profound experience of the natural world creates a sense of authenticity that is lacking in the rest of the novel.
The most grounded characters in The Sun Also Rises share a sense of appreciation and an innate understanding of nature.