Although she does not use the term, Amy Tan’s “Mother Tongue” is a classic description of code-switching, the practice of switching between different languages, dialects, styles, or registers according to the situation and people being addressed. Tan writes early in “Mother Tongue” that as a writer, language is the tool of her trade, and she has learned to use all of the Englishes she grew up with to enrich her work.

At school, she learned standard English, which she uses in formal situations and which she used exclusively when she started writing fiction. With her mother, however, she has always used a different form of English, more direct and expressive, often ignoring the grammatical rules of standard English. Tan says that she was recently talking to her mother about buying furniture and found herself saying, “Not waste money that way.” Although her husband, who regularly hears Tan speak standard English in other situations, was with them, neither he nor Tan noticed any switch in her English. Tan then realized why this was:

It’s because over the twenty years we’ve been together I’ve often used that same kind of English with him, and sometimes he even uses it with me. It has become our language of intimacy, a different sort of English that relates to family talk, the language I grew up with.

Tan says that she did not particularly enjoy or excel in English classes at school, since the exercises she had to complete seemed banal and boring to her, their predictability at odds with the color and vibrancy of her mother’s idiosyncratic English. At the same time, she was ashamed of what she saw as her mother’s “broken” English, a term she now dislikes because it implies that her mother’s English needs to be fixed, “as if it lacked a certain wholeness and soundness.” Because of this embarrassment, Tan rejected her mother’s style of speech and, when she first became a writer, tried to write exclusively in the formal English she had learned at school and college. This changed when her writing about mothers made her think that she should write a book her own mother could read. Tan’s mother read the early drafts of her work and she came to see that using all the different Englishes at her disposal strengthened her as a writer. She knew she had succeeded when her mother gave the verdict on her book: “So easy to read.”

Amy Tan admits that while she was growing up, she was often ashamed of her mother’s way of speaking English, particularly in public settings. She gives two examples of the ways in which American society prejudges non-native speakers of English. Both examples illustrate that her mother internalized the prejudice against the way she spoke and “realized the limitations of her English.”

In the first instance, Tan pretended to be her mother in a telephone conversation with a stockbroker who had failed to send a check on time. When the matter was not resolved, the two of them visited the stockbroker in his New York offices, and he was astonished to hear his actual client “shouting at his boss in her impeccable broken English.” Tan observes that her mother is a woman of considerable financial acumen—she listens to Wall Street Week and reads the Forbes report—but her way of speaking English leads others to underestimate her.

The second instance of discrimination occurred just a few days before Tan wrote the essay. Tan’s mother had gone to the hospital to find out about a benign brain tumor that...