The question of tone is notoriously tricky in Heart of Darkness, particularly because of Conrad’s use of a frame story. It is very easy for the reader to forget about this framing structure and to think about Marlow’s tale only. However, the frame narrative provides the reader with an opportunity to step back from Marlow’s tale and evaluate the man and his story from a distance. Marlow himself admits this when he pauses and reflects on his story to his fellow passengers: “Of course in this you fellows see more than I could then. You see me, whom you know.” For this reason, students of the novella must think about tone on two levels: the tone of Marlow’s tale, and the tone of the frame narrator’s tale. 

The tone of Marlow’s tale is ambivalent, meaning that it expresses contradictory attitudes that remain unresolved. In particular, Marlow’s narrative expresses contradictory attitudes about imperialism. This contradiction appears at the very beginning of his narrative, when he condemns the brutality of empire, which he characterizes as “just robbery with violence.” By contrast, Marlow believes that the project of colonialism can be redeemed. What distinguishes colonialism from imperialism is, according to Marlow, the ideal of efficiency. Unlike imperialism, which involves the powerful taking control of the weak and ruling over them, colonialism involves the extraction of resources and honors values like productivity, travel, and exchange. This is why Marlow asserts that “the conquest of the earth,” which is repulsive when examined too closely, can be redeemed by the “idea” at its core. It should be emphasized that Marlow’s distinction between imperialism and colonialism is not a technical one, but an ideological one. As an Englishman, Marlow seems interested in justifying British colonialism by distinguishing it from the comparatively more brutal Belgian example. But the difference between British and Belgian colonialism is one of degree, not kind. Hence, Marlow’s ambivalence points to a deeper uncertainty about whether colonialism is defensible. 

The frame narrative’s tone is also ambivalent, but in a slightly different way. Whereas Marlow is ambivalent about imperialism, the frame narrator is ambivalent about Marlow himself. When Marlow begins to speak, talking about Roman imperialism and about how England itself has also “been one of the dark places of the earth,” his companions do not seem interested; no one even bothers to grunt in response. Nevertheless, Marlow tells his story anyway. The narrator concludes that by doing so, Marlow demonstrates “the weakness of many tellers of tales who seem so often unaware of what their audience would best like to hear.” The narrator’s remark is ironic, and it clearly comes from a sense a familiarity: “It was just like Marlow,” he says, referencing the morose statement his companion has just made. Although the frame narrator does not characterize Marlow as a bad or repulsive person, the fact that no one wants to hear his story certainly has a distancing effect on the reader. Why should the reader continue if none of Marlow’s fictional audience wants to listen? Will his tale be remorselessly pessimistic? These kinds of questions point to the ambivalence of the frame narrator’s tone.