Early in the novel, Nick uses metaphors to compare Long Island’s two northern peninsulas to eggs and Long Island Sound to a barnyard:
Twenty miles from the city a pair of enormous eggs, identical in contour and separated only by a courtesy bay, jut out into the most domesticated body of salt water in the Western hemisphere, the great wet barnyard of Long Island Sound.
The “pair of enormous eggs” are a metaphor for the aptly named East Egg and West Egg, two peninsulas on the northern coast of Long Island. Comparing these areas to eggs gives the sense that these two places are symmetrical and tidy, like smooth eggs; the land is just as polished as the wealthy residents who live on the peninsulas’ waterfront mansions.
The “eggs” also appear identical, which suggests that, at least from an outsider’s perspective, there isn’t much difference between the people who live on the respective sides of the bay. However, the “old money” residents of East Egg (like Tom and Daisy Buchanan) certainly want to distinguish themselves from the “new money” residents of West Egg (like Jay Gatsby). The fact that there is a bay physically dividing these two “eggs” further implies that there is social division between the east and west sides.
Moreover, using the metaphor of a “great wet barnyard” to describe Long Island Sound subtly suggests that this affluent area isn’t as idyllic as it might initially seem. A “wet barnyard” connotes dirtiness and foul odors, implying that for all the prosperity and glamour of East Egg and West Egg’s residents, there is underlying conflict and immorality rotting beneath the surface. All in all, then, this initial description of Long Island hints that the American Dream of success and wealth—which those who live on the Eggs seem to have achieved—may not be as enviable as it seems.
Nick’s thoughts during his first dinner with the Buchanans contain an implied metaphor comparing Tom to an animal nibbling on stale food:
As for Tom, the fact that he “had some woman in New York” was really less surprising than that he had been depressed by a book. Something was making him nibble at the edge of stale ideas as if his sturdy physical egotism no longer nourished his peremptory heart.
The book Nick is referring to here is The Rise of the Colored Empires, whose central argument is that white people are inherently superior to other races, and that non-white people’s success poses a threat to white people’s deserved dominance over other groups. The idea that Tom is “nibbl[ing] at the edge” of the “stale ideas” that he reads likens Tom to an animal trying to get nourishment from something that’s old and unappetizing—that is, a racist, pseudoscientific book.
Nick suggests that Tom might be attracted to white supremacist ideology because “his sturdy physical egotism no longer nourished his peremptory heart.” In other words, something in his life has made him feel less confident than he was before, and convincing himself that he’s part of a master race makes Tom feel better about himself. This could be rooted in the fact that Tom “ha[s] some woman in New York” (meaning that he’s cheating on his wife, Daisy), and he feels insecure and nervous that Daisy will find out about his mistress. This metaphor thus suggests that people who behave selfishly and immorally tend to seek out information or belief systems that will bolster their egos and ease their guilt—even if those beliefs are “stale” and outdated—like hungry rodents desperately trying to nourish themselves with scraps of old food.
The Great Gatsby’s famous last line is an example of both metaphor and alliteration:
So we beat on, boats against the current, borne back ceaselessly into the past.
First, the passage uses metaphor to compare people (both the novel’s characters and Americans more generally) to boats that are propelled into the past despite their efforts to move forward into the future. Typically, boats move with the current, not against it—a current is usually thought of as something that propels things forward to their destination. Yet here, the boats are rowing “against the current,” meaning that the water is forcing them backwards. So, with this metaphor, the novel is suggesting that even as people try to move forward and embrace the present and future (i.e., as they chase their dreams), they will nonetheless be unable to ever fully escape the impact of their past.
This idea complicates Nick’s earlier claim in the novel that “you can’t repeat the past”—advice that Gatsby ignored as he shaped his entire life around impressing Daisy to win her back and recreate their youthful romance. The metaphor in this passage instead pessimistically suggests that you can’t escape your past—that even as people look forward to the future, doing so will paradoxically entrench them in the past. This is because even dreams and future goals—be it a dream like Gatsby’s or, more generally, the American Dream of success—are tied to recreating an idealized version of the past. Such an idealized vision can never be perfectly recreated (because it never even existed), but it also can’t be escaped because of its idealized perfection. The novel implies that this dynamic is true not only of Gatsby, but of the U.S. more generally, as the novel’s tragic end suggests that the boundless optimism and rapid progress of the Roaring Twenties will itself fade away as history inevitably repeats itself. The Great Gatsby was published in 1925, but this prophecy arguably came true, since the 1920s were immediately followed by the Great Depression and then by World War II.
The alliteration in this passage serves to deepen the metaphor. The hard “b” sound in “beat,” “boats,” “borne,” and “back” is meant to sound harsh and persistent, reflecting at once both the rhythm of the boat’s oars hitting the water and the chaotic image of the boats trying desperately to row forward while the turbulent sea propels them backward. The alliteration thus emphasizes the persistence and optimism of those who seek to fulfill or create their visions of the future, while also capturing the way that such efforts are self-destructive and futile.