To avoid confusion, writers often use word repetition. The device of repeating words and phrases is especially helpful if a pronoun might confuse readers:
Some odd optical property of our highly polarized and unequal society makes the poor almost invisible to their economic superiors. The poor can see the affluent easily enough—on television, for example, or on the covers of magazines. But the affluent rarely see the poor or, if they do catch sight of them in some public space, rarely know what they’re seeing, since—thanks to consignment stores and, yes, Wal-Mart— the poor are usually able to disguise themselves as members of the more comfortable classes.
—BARBARA EHRENREICH, Nickel and Dimed
Repeated words
In the next example, several overlapping chains of word repetition prevent confusion and help the reader follow the ideas:
Natural selection is the central concept of Darwinian theory—the fittest survive and spread their favored traits through populations. Natural selection is defined by Spencer’s phrase “survival of the fittest,” but what does this famous bit of jargon really mean? Who are the fittest? And how is “fitness” defined? We often read that fitness involves no more than “differential reproductive success”—the production of more surviving offspring than other competing members of the population. Whoa! cries Bethell, as many others have before him. This formulation defines fitness in terms of survival only. The crucial phrase of natural selection means no more than “the survival of those who survive”—a vacuous tautology. (A tautology is a phrase—like “my father is a man”—containing no information in the predicate [“a man”] not inherent in the subject [“my father”]. Tautologies are fine as definitions, but not as testable scientific statements—there can be nothing to test in a statement true by definition.)
—STEPHEN JAY GOULD, Ever Since Darwin
Repeated words with some variation of form