As the crew make their way up the river, they are travelling into the "heart of darkness". The contradiction, however, is that Marlow also feels as if he were travelling back in time. When Conrad wrote this story, scientists were learning that Africa is the seat of human civilization, and this knowledge is reflected in the fact that the enormous trees on the route down the river are almost prehistoric. The paradox of the novel, however, is that by travelling backwards in time, the crew do not move closer to the innocence and purity of the "noble savage" but farther away from it. Conrad seems to claim that the Christian belief that prehistory was untouched by obscurity or evil is a fallacy. Instead, there is "the horror". In contrast, its seems, is the more advanced civilization of the colonizers and visitors.
3. Pervasiveness of Darkness
Perhaps the strongest theme in the novel is that of darkness. Indeed, darkness seems to pervade the whole work. Marlow's tale begins and ends in literal darkness; the setting of the novel is often dark, such as when the steamboat is socked in by fog or when Marlow retrieves Kurtz; dark-skinned individuals inhabit the entire region, and, of course, there is a certain philosophical darkness that permeates the work. But within the tale darkness operates in several ways. Moreover, darkness creates fear and conceals certain savage acts. It is too enveloping. The character who most fully embraces the darkness is, of course, Kurtz. This theme suggests that the light of civilization will someday return to darkness.
Nothing in the novel is described in concrete terms. Shores are hazy. Land looks like a spine sticking out from a man's back but is not described in topographical terms. Marlow is obsessed with Kurtz before he even meets him, without a clear idea why. A sense of danger pervades the entire trip, and it is mostly dictated by uncertainty. The natives do not seem inherently threatening. On one occasion, they let fly a series of arrows, but these even look ineffectual to Marlow. They are threatening because they might be poisoned. Similarly, Marlow has no clear idea of what the natives might do to him if Kurtz gave them free rein. Kurtz himself is an uncertain figure, ruled as he is by two separate impulses, the noble and the destructive. Above all, the idea of "darkness" expresses the theme of uncertainty.
Whatever the conditions in Africa may be, all of the characters agree that they are different from those of Europe. There is a feeling of anything-goes vigilantism that shifts the balance of power from the stewards in a "civilized" state to whoever is most threatening. Kurtz is physically quite a weak man, but he maintains enormous sway over the native population through his understanding of their language and his cultural and communication skill. He exploits their appreciation of him as an Other. Marlow's men use a much more simple means of gaining authority, namely, firearms. This is the tragedy of imperialism in that the arrival of the white man heralds a new order, but in the creation of that order, they retain the tools and the authority. Black men in this book first appear as members of a chain gang, and they gain little power after that scene.
Although there is controversy over whether Conrad is critiquing colonialism or not, it is clear that he is critiquing religion. The two groups in the novel, the pilgrims and the natives, are linked by having religious beliefs, and the pilgrims seem at least as bloodthirsty as the natives. The rite in the woods that Marlow describes seems alien but certainly no more dangerous than the ambush. One of the seemingly admirable characteristics of Kurtz, as presented by Conrad, is that he seems just as compelled by African religion as by Christianity but seems beholden to neither. Marlow genuinely admires his ability to independently critique religions. He may not agree with Kurtz's evaluation, but he respects Kurtz's ability to have his own opinions in the face of the various religious traditions he encounters.
Illness is a major factor in this novel. It appears in physical and mental forms. Marlow is hired to replace a man who committed suicide, and another instance of suicide is announced by a somber Swedish man. The first thing that Marlow does upon being hired is to to to the doctor, who checks both his mental and physical health and provides a very gloomy prognosis. The specter of ill health, or of one's body not standing up to the conditions, is a constant specter in the novel. The mental health issue is particular to "Heart of Darkness", while the issue of wider health continues in the tradition of Victorian novels, in which men often travel to Africa only to come down with exotic diseases. In the end, it seems that Marlow is more mentally than physically taxed, while Kurtz is clearly both.
The white pilgrims go into the interior in constant fear of their surroundings. Their trepidation is so strong that they develop a paranoia of the wilderness -- its eerie silences and sudden blinding fogs, its impenetrable darkness and shadowy savages. Being so far removed from any vestige of civilization as they know it only adds to their sense of helplessness. Their fear makes them do foolish things on impulse. Fear also contributes to their eventual madness. It pervades the entire novel and seems to seep into the environment itself so that everything is not only terror-inducing, but morally disturbing as well.
The novel depicts European society as hollow at the core: Marlow describes the white men he meets in Africa, from the General Manager to Kurtz, as empty, and refers to the unnamed European city as the "sepulchral city". Throughout the novel, Marlow argues that what Europeans call "civilization" is superficial, a mask created by fear of the law and public shame that hides a dark heart, just as a beautiful white sepulcher hides the decaying dead inside. In the African jungle -- "utter solitude without a policeman" -- the civilized man is plunged into a world without superficial restrictions, and the mad desire for power comes to dominate him. So when Kurz suddenly finds himself in the solitude of the jungle and hears the whisperings of his dark impulses, he is unable to combat them and becomes a monster.
The novel is an exploration of hypocrisy, ambiguity, and moral confusion. It explodes the idea of the proverbial choice between the lesser of two evils. As the idealistic Marlow is forced to align himself with either the hypocritical and malicious colonial bureaucracy or the openly malevolent, rule-defying Kurtz, it becomes increasingly clear that to try to judge either alternative is an act of folly. The number of situations Marlow witnesses act as reflections of the larger issue: at one station, for instance, he sees a man trying to carry water in a bucket with a large hole in it. At the Outer Station, he watches native labourers blast away at a hillside with no particular goal in mind. The absurd involves both insignificant silliness and life-or-death issues, often simultaneously.