Class Conflict
As the socialist stoker, Long tells his fellow workers in a brief soapbox speech, and Yank personally when the two visit Madison Avenue in New York, that he believes they should realize the terrible state of their living and working conditions, and realize the societal forces that determine them. According to Long, who is portrayed by O'Neill as a one-dimensional, ideology-defined character, everything that is wrong in the lives of the workers is the fault of the capitalist class, whom they should therefore overthrow. Yank—and one senses O'Neill himself—is averse by disposition to any view that accepts that there are forces outside of oneself that one cannot overcome by blunt force, but because of this he comes up with a truly bizarre idea: "I mean blow up de factory, de woiks, where he makes de steel. Dat's what I'm after—to blow up de steel, knock all de steel in de woild up to de moon. Dat'll fix tings" (82). As the Wobblies who throw him out on to the street after hearing this know, this sort of thinking is almost a parody of the socialist work they do.
Suspicion Against Ideologies
One of the defining facets of Yank's individualism is that he does not believe in anything except his own strength. When other people have ideas that seem too sophisticated and conceptual, especially when they try to explain suffering in the world, Yank can only see them as weak and cowardly. After Long's socialist speech, Yank reacts with great sarcasm and contempt: "De Bible, huh? De Cap'tlist class, huh? Aw nix on dat Salvation Army-Socialist bull. Git a soapbox! Hire a hall! Come and be saved, huh? Jerk us to Jesus, huh? Aw g'wan! I've listened to lots of guys like you, see. Yuh're all wrong. Wanter know what I t'ink? Yuh ain't no good for no one. Yuh're de bunk. Yuh ain't got no noive, get me? Yuh're yellow, dat's what. Yellow, dat's you" (44). Yank hasn't actually made an argued rebuttal, but like a bully, he has silenced and humiliated Long just by sheer force.
Mechanization and Dehumanization
At the end of his long elegy to the past age of sailing, Paddy levels a challenge to the machine-loving Yank, posing against the latter's modernist faith in the empowering potential of the machine a romantic respect for a kind of essential humanity. Yank contemptuously rejects Paddy's ideas at first, but then throughout the rest of the play he comes to realize that machine civilization in fact deprives him of his power and furthermore of his humanity. Yank is only able to see the truth of the importance Paddy places on basic humanity when he has already lost it himself; by that point Yank thinks despairing that he has had none to begin with.
Male Camaraderie
Although Yank is a dogged individualist and a man confident in the powers of his own body, O'Neill makes it clear to us that not only is he dependent on machines, which eventually emasculate him, but also the affirmation of his fellow working men, who eventually abandon him. Yank himself only realizes this too late, when he is thrown out of the IWW meeting; in a sense, he has taken masculinity to so extreme an extent that he alienates those men whom he used to impress and stand before as a model.
Alienation of Labor
Karl Marx in his Economic and Philosophical Manuscripts of 1844 famously described how labor/work means something entirely different for workers in modern capitalistic society in contrast to premodern workers. On the steamship, even though Yank and the other stokers may feel a great sense of confidence in their own physical strength, they do not own the furnaces they feed, let alone the entire transatlantic liner. Thus, they are dependent upon the business owners in order to be able to have work at all. Moreover, the product of their work does not really go to the end of sustaining themselves; the ship takes its passengers across the Atlantic, but the stokers must stay, as opposed to a farmer who plants to feed his family.
Mockery
O'Neill is known as a very dark playwright who broods on the conditions of abjection and despair, but this is at once tempered and deepened by his acerbic wit. In The Hairy Ape, even though Yank is one of the least educated characters and certainly the one who values cerebral intelligence the least, he is also the one in whom O'Neill invests his most powerful sarcasm. Yank does not just beat up others to assert dominance over them; with a kind of laugh of superiority, which French poet Charles Baudelaire described in his essay "On the Nature of Laughter," Yank maintains his position mainly by a combination of mockery and threats. Just how essential these were to his character can be heard in his very last words, which almost address the audience directly, mocking them as carnival-goers and mocking himself as a hapless caged ape.
Historical Change
The character of Paddy serves as both a kind of father figure and a foil to Yank. Having worked on sail ships in an age before steamships, in which sailors felt themselves both much more actively involved in the mechanics and processes of the ship and closer to the nature they traversed, Paddy is more aware than the younger man of the changes wrought upon the sailing experience by the introduction of modern mechanization. He tries to impress this higher perspective of historical difference upon Yank, but the latter is too absorbed in the ecstasy of present strength to realize, until it is too late, the old man's lesson: the machine invigorates, but it also dominates and cages.
Social Darwinism
The worldview espoused by Yank, even though it may seem to smack of classical Greek tragic heroism, is driven by a kind of aggressively modern ideology that finds one of its most frightening expressions in the idea of Social Darwinism. Twisting the contingent and purposeless notion of natural selection and fitness that Charles Darwin introduced in his On the Origin of Species (1859), Herbert Spencer and others saw evolution as a life-or-death competition of strength in which only the strong would survive; significant is the secularism of this worldview, in which everything is reduced to natural phenomena and no higher ideals remain. For Yank, so long as he feels like the top dog, his world seems to function perfectly; however, once he finds himself in a position of impotence—the sort of situation for which he would have mercilessly criticized another—he implicitly senses the emptiness of the way he looks at life.