Why are most of the characters identified by title or description? Give some examples of these characters and explain their roles in the story.

Marlow's use of titles rather than names over the course of the narration speaks to their importance in his story. The people he meets along the way aren't firends, they're workers, and he treats them as such. Outside of their job descriptions, he doesn't find them important enough to name..... it is similar to telling someone a story and using the word neighbor, teacher or even cousin..... their names don't serve a purpose in making your point or moving the plot along, so you refer to them in a more generalized way.