Nature as a force - When he travels from station to station, Marlow observes the scenery around him and consistently describes the wilderness as giving him an uneasy feeling. He depicts nature in a way that makes it seem impenetrable and imposing, yet describes it as an ongoing force that sits still in the background, watching everything take place. To Marlow, the tranquility of the jungle is not peaceful, but rather foreboding and ominous. Marlow's reflection is meant to remind himself and the reader about the futility of humankind and that our efforts are much less impactful when compared to the everlasting grandness of nature.
Greed - the power of greed weighs down on the entire story immensely. It is present among the pilgrims, who are so religiously devoted to ivory that this is what earned them this nickname by Marlow. When Marlow firsts lays his eyes upon them he is disturbed by their lack of drive to actually do anything other than want riches and hate others for having them. It's a criticism of the Company men that can be applied to the European society this story displayed as well as the modern society today. The consequence of greed on a man are displayed, however, in Mr. Kurtz's corruption. He isn't literally killed by greed, but his devotion to ivory and lack of willingness to leave the Congo is what ultimately causes him to die there.
Inhumanity - the inhumanity that the white men display not only toward the natives, but toward themselves is staggering. They treat the natives as savage animals and show their attitude towards black people as supbar. Meanwhile, the pilgrims and Company men are so caught up in their noble cause, their quest for riches, that the turn on one another out of jealousy and hatred. This is most apparent when the leader of the Eldorado Exploring Expedition speaks to the manager of the Central Station. He tells him to hang another traveler that simply annoys him and to display his body for everyone to see. Proposing such a cruel punishment for someone that merely inconveniences you is an absolute form of inhumanity and shows how far gone nearly all of the white men in the Congo were.
Darkness - throughout the novella, Marlow describes his settings to be completely surrounded by darkness. There is darkness everywhere: in the forests, the cabins, the stations. It appears to be a mysterious and corrupting force, bringing out the worst of men's desires and hatred while also enveloping them with the unknown. To Marlow, the darkness is what he cannot see, and thus, what he cannot understand. Darkness follows him wherever he goes because he cannot understand himself nor the nature of people around him. He fails to truly understand the natives and is also baffled by how the white workers are so consumed with greed. It is a general misunderstanding and lack of knowledge of the country around him that he fears.
Ivory - in the book, ivory is both a literal form of wealth, while simultaneously symbolizing the materialistic greed of the white workers there. Ivory is present at the heart of darkness, the Inner Station where Mr. Kurtz lies. However, Ivory is also present in many of the conversations of the pilgrims and company men, showing its extent beyond a place of pure corruption to the many Company stations present in the Congo.
Savagery - the customs and behaviors of the natives is described as savagery by Marlow numerous times. Its most distinct recount was when Marlow is traveling along the river and hears the sorrowful cries of the native people. He recognizes them as savage, yet comes quite close enough to relating to them on a human level. He fails to understand that he could do this if he just viewed them as more than savages, as humans. But nonetheless, savagery is the term used by Europeans to describe customs so different from theirs that they must be inferior and primal. This attitude is consistent throughout the book and it reflects the thoughts that European societies held of colored people at the time.
The steamboats - the steamboat that Marlow is a passenger on as well as captains represents his connection to the waters as well as a means of escape from the environment around him. When Marlow drives the boat along the river, he physically separates himself from the trees and the people along the banks. We already understand that Marlow is uncomfortable with the scenery surrounding him, and to him, his steamboat is a shuttle that allows him to travel and distance himself from the terrible and mysterious things taking place in the Congo. Also, he sleeps in the ship when it is disrepaired at the Central Station, further proving the ship's purpose of being a place of refuge and comfort for Marlow.
The painting in the first-class agent's cabin - when Marlow speaks with the first-class agent in his house at the Central Station, he asks about a painting of a blindfolded woman holding a torch in a dark setting. The agent tells him that Kurtz painted the image a year ago while he was at that very station, before he left for the Inner Station. The painting represents Kurtz's attitude about his journey there. As we read, we come to realize that Kurtz is the physical embodiment of what many Europeans were trying to establish in the Congo and in other colonized areas around the world. Under the scene of trading systems, they were also trying to impose their ideas of progress and intellectualism on the 'unenlightened' civilizations that already lived there. Kurtz paints the woman to represent himself, walking blindly through the darkness of Africa holding a torch: a beacon of hope and progress in a land full of mystery and savages. This interpretation of himself shows that many Europeans of the time considered such an act to be noble, whether they realized what they were doing was cruel or not.
Flies - in the book, flies are always present near a man who is approaching death. The first instance was in the chief accountant's office at the first company station Marlow visits, where there are flies buzzing around the room and the sick man staying there. The next instance was near the end of the story where there are flies swarming the mess hall before Mr. Kurtz is pronounced dead. Coincidentally enough, the flies only surround men infected with disease.