In the introduction to the reader in Chapter One of To Kill a Mockingbird, Scout relates the history of her family, the neighbors, Dill, and the Radleys. After explaining how Boo Radley was kept in his home because he had been running around with the Cunninghams and had committed some mischief, Scout repeats the legend of the thirty-year-old Boo's having impaled his father's leg with a scissors one day as he sat on the floor cutting the newspaper. The sherriff was called to the house, and not having the heart to put Boo in a cell with others, he placed Boo in the basement. When the father refused to retrieve him, Mr. Radley was pressured to take his son from the damp cellar of the jailhouse. So, Mr. Radley does, but
Nobody knew what form of intimidation Mr. Radley employed to keep Boo out of sight, but Jem figured Mr. Radley kept him chained to the bed. Atticus said no, it wasn't that sort of thing; there were other ways of making people into ghosts.
The implication by Atticus with this statement is that Mr. Radley did not physically restrain Boo. Instead, he isolated Boo, refusing to allow him to go outside or be seen in public. Away from the community, the memory of Boo as a real person fades, and he becomes a "ghost," only a gossamer shape who once tread the streets of Maycomb, now a mere shadow of a person in the minds of the townspeople.
This statement of Atticus about Boo Radley evokes William Faulkner's character of Emily Grierson, who sequestered herself in the old mansion. In her absence, the people of Miss Emily's town imagined her "an institution" and not as a woman. Similarly, Boo Radley is imagined as a "malevolent phantom" who comes out at night and peeps in windows and freezes azaleas by breathing upon them.