Colonialism
Even though the subject of colonialism is not specifically dealt with in this novel, it is still pervasive and significant. The events of the novel take place in the last days of the British reign in Nigeria and reveal the tensions present between white and black society, politics, religion, and character. Achebe has very strong views on colonialism, quite obviously, and expresses them in the novel through his condemnation of whites as either grotesque, cruel, ignorant, or immoral, as well as his depiction of the negative impact white culture has on Nigerians (such as Obi). The Nigerians are clearly superior to their colonizers in their values and social mores and norms, but they still must navigate the waters of being second-class citizens in their own country. Every choice makes or has made for him is a product of colonialism.
Identity
Obi’s background, the legacy of colonialism, and his own character and choices shape his identity. He comes from a heritage that values community, loyalty, and tradition, but moves away from those things. He takes a stand on some things, such as not accepting bribes and staying with Clara, but proves unable to sustain those commitments. He is weak, prideful, and ignorant. He is full of excuses for himself, and even in his moment of clarity that he thinks he has, does not truly get at the root of his inaction, his lack of a moral center. By the time the novel comes to a close, Obi's growth as a character appears limited, if visible at all. He claims to not want to take bribes anymore, but his identity is still nebulous. It is unclear where he will go after this, as he has no great passion, no great goals or strong beliefs.
Culture
Achebe contrasts white and black culture in his novels. Here, white, English culture is depicted as soulless, deadening, immoral, and Nigerian culture is depicted as authentic, uplifting, and sustaining. Drinking, sex, dancing, and bribery are all associated with the white man's world, and the white neighborhood where Obi lives in Lagos is compared to a graveyard. Obi and his father love the written word of the whites, which, as symbolized by mounds of paper, is full of sound and fury. Nigerian culture is associated with a valuing of the past, communal support, tradition, and loyalty. However, for all of his touting of the values of Nigerian culture, Achebe does acknowledge that it is very much mired in the past and cannot yet evolve; Joseph calls himself and Obi "pioneers", and Obi realizes how ridiculous it is to either pay for a wife or be denied marriage to a wife of one's choosing. Obi is caught between two cultures, wherein lie his difficulties.
Corruption
Corruption seems to be rife within the senior service, and, indeed, within the colonial bureaucracy as a whole. It is commonly assumed that bribery is something everyone does, both in white and black circles. There are several attempts to bribe Obi before he actually accepts it. The fact that Achebe opens his novel with the scene of Obi's trial reinforces the centrality of the issue. What is tragic, though, is that Obi did hold out for much longer than most, and his trial is practically a show trial since he is clearly a scapegoat and many, many others are guilty of bribes. The indignation rings rather false, as Achebe suggests. Obi's views on younger civil servants replacing older ones does not seem to hold up, as he himself obviates the theory. Achebe does not condemn Obi as much for this as his other traits, however, and seems to suggest that it was almost inevitable given the deleterious effects of colonialism.
Hypocrisy
Hypocrisy is rife throughout the novel, mostly displayed in the words and actions of the English. Mr. Green scoffs at the corruption of Nigerians, in particular with their acceptance of bribes and, later, Obi's taking time off, but clearly the English are also heavy on bribery and indulgence. Obi even remarks to Miss Tomlinson that the English set up the time-off situation to benefit themselves, and then loudly complained when Nigerians were able to take advantage of it. The English love to complain about the Nigerians for the same things they do themselves or claim to value.
Morality
Achebe mostly associates morality with the Umuofians, as opposed to the English. Obi's moral downfall, which entails his loss of connection to his hometown and his family, his consorting with louche characters, his impregnating and leaving Clara, his financial mistakes, his pride and his ignorance, and, of course, his acceptance of bribes, are both a result of his own character and the situation in which he navigates. That situation itself is informed by the legacy of colonialism, which made bribes commonplace, supported hypocrisy and incompetence, and encouraged young Nigerians to find value and power in the white man's world.
Education
Throughout the novel education is presented as something desirable to attain. Obi is depicted almost as the savior of his village when he gets the scholarship to go abroad. People nearly prostrate themselves before him trying to get him to recommend them or some loved one to the scholarship board. Those like the Hon. Sam Okoli are clearly very educated and may have something to offer Nigeria as it moves away from colonialism. Achebe is also hesitant about education, though, because he knows that one of its concomitants is a loss of connection to one's roots. Obi has difficulty with the language, with the appropriate mannerisms and wardrobe, and generally with understanding what his people want/need. Embracing education often means embracing the white man's world, which Achebe cautions against doing so naively.