There is a significant tonal shift in "Cathedral" as the narrator and Robert begin to draw together. How would you describe the tone of Carver’s writing here? How does the change in tone affect the way we see the relationship between these characters?

Tone is defined as the author’s attitude toward the subject of the text. If the subject is the narrator’s attitude toward Robert, his wife’s blind friend, then one needs to describe it in two separate terms.
For the majority of the story, the narrator is annoyed at the idea of Robert, mostly because his wife has confided in the blind man for years. When he meets Robert, he observes with judgment several details of the blind man’s appearance that seem out of sync with the stereotypical idea the narrator had in mind prior to their meeting. These include Robert’s beard and the movement of his eyes. This tone suggests that the narrator didn’t really view Robert as a person equal to himself.
Once Robert and the narrator talk after the wife falls asleep, this tone shifts. The narrator feels a sense of responsibility for explaining what is happening on television, saying he felt like he was doing a bad job. He also eagerly answers Robert’s questions and even agrees to the drawing exercise. While drawing, the narrator feels powerful and happy. Overall, the tone could be described as open.
This tone shift affects the way readers interpret the relationship between the narrator and Robert. When the narrator feels disdain or irritation toward Robert in the beginning, the reader infers that the narrator may be jealous of the relationship Robert has with the narrator’s wife. By the end of the story, however, the narrator’s changed attitude indicates a feeling of trust and friendship, suggesting to the reader that perhaps the narrator just didn’t understand why his wife liked Robert so much.