Since there is not much physical description or even speech, Conrad develops most of his characters through action. As the protagonist, Marlow receives a great deal more interior consistency than most of the other characters. The accountant, the manager, the brickmaker, and even Kurtz show a great divide between what they say and what they do. Often, their actions are far more indicative of their true character than their speech.
We know a lot about Marlow because of what the peripheral, nameless narrator tells us. "Marlow was not typical," he explains. He goes on to detail Marlow’s story-telling beliefs, that "to him the meaning of an episode was not inside like a kernel but outside" and so on and so on in this rather poetic and hugely important passage.
Did you notice that no one around here seems to have a name? Besides Marlow and Kurtz, that is. Everyone else just has a title/profession: the accountant, the harlequin, the manager, the Intended. It could be that this illustrates the dehumanization of men in the wilderness of the Congo. If this is true, then what’s so human about Marlow and Kurtz? At the most elementary level, names are used to highlight the importance of Marlow and Kurtz above all other characters. But we think there must be more to it. Have at it.
Since Marlow is the narrator, we get mostly his speech and thoughts in his specific vernacular, which is rife with British witticisms. As a general rule, only the white people speak and their speech is given in standard English. Some of the characters – namely the brickmaker and the harlequin – have rather erratic speech. Their speeches are often marked with hyphens, showing a good deal of hesitation and uncertainty.
For the most part, black slaves and native Africans do not speak, at least not English. There are some instances where they communicate nonverbally, through ritualized gestures or loud emotional cries. However, these are highly unintelligible to Marlow, save for the exceptional occasions when overwhelming emotion graces their voices. However, readers often find that the Africans have a more effective way of communicating than Marlow and crew’s manner of speaking.
Occasionally, a black slave (such as the manager’s boy) or a cannibal speaks in English to communicate vital information to Marlow. Their English is always marked with heavy accents and, often, with incorrect grammar. Their speaking has a distinctly pidgin feel to it and highlights their inability to completely function in the white man’s world.