FRENCH LESSONS A Memoir. By Alice Kaplan. 221 pp. Chicago: University of Chicago Press. $19.95.

"I HAD never heard my grandmother speak more than a sentence or two in a foreign language until she lost her mind," Alice Kaplan tells us at the beginning of her engaging memoir, "French Lessons." Her grandmother's madness, she remembers, was awash with babel: Yiddish from home, Hebrew from synagogue, Russian from school. "The change from one language to another, from ritual to conversation, was all the communication she could produce."

Ms. Kaplan's immigrant family had, in one quick generation, shed not only the language of their forebears, but its appurtenances as well. Ensconced in an old, white-shoe Minneapolis neighborhood, she grew up speaking Midwestern without the shadow of an accent. And she grew up in an America -- the America of the 1950's -- where the very idea of foreignness was alien -- remote in a way it will probably never be again. "It seems now," she reflects, "that no one will ever again have that sense of being American that we had then, in the time between the Second World War and Vietnam."

In one of the ironic reversals generations so often undergo, the emblem of her grandmother's madness became Ms. Kaplan's salvation. Sent to boarding school in Switzerland at the age of 15 to get over her father's death, she rescues herself by learning to live in another language. Initially, what draws her to French is the sense of control she derives from conquering the impossible French "r" -- a speech exercise beyond the pale for most Midwesterners. But later on, it is the possibility of escape -- the possibility of becoming someone else -- that attracts her.

Learning French allowed Ms. Kaplan to put her world into order, which in its turn awakened her to the pleasure of intellectual discovery. "That was what woke me up," she writes in "French Lessons," "absorbing a new reality, repeating it, describing it, appreciating it. . . . Knowing how to find out more. Inventing methods for listening. . . . Then the pleasure of writing down what I had heard and getting every detail, every accent mark right."

By the time she returned to the United States, Alice Kaplan had fallen irretrievably under the spell of her adopted language. "French Lessons" examines the consequences of her infatuation and its evolution into a career as a teacher. Along the way, she offers useful advice for coming to grips with the most daunting of French sounds, those that separate the barbarians from the chosen. To get the "r," practice gargling with mouthwash. To find the "u" of "tu," Ms. Kaplan instructs: first, "say 'o' with your mouth in a perfect round," then " 'eee' with your mouth stretched out in a horizontal smile like a trout," then a combination of the two.

ANYONE who has ever struggled with these two intractables and come out the victor will feel a frisson of recognition reading her description of what it felt like: "First feeling them wrong, like an impediment, feeling them again and again in their wrongness and then, one day, opening up and letting the right sound come."

Though less compelling than the earlier autobiographical chapters, Ms. Kaplan's description of her career as a graduate student at Yale in the 70's is instructive. Yale, under the guiding light of Paul de Man, was at the cutting edge of deconstructionism, which in its turn was the avant-garde of French literary studies. She recalls the heady experience of discovering a new way of reading, whose premise was that "language can never tell the whole truth."

Surrounded by theorists who eschewed historical context, Ms. Kaplan chose to work on a subject that "made history impossible to ignore": fascist propaganda of World War II. Her initial impulse was to "transgress a purity that I mistrusted in literary studies." The irony of her decision was apparent only years later, when Ms. Kaplan heard that Paul de Man, the man who had taught her to separate literature and life, had written for the pro-Nazi press in wartime Belgium.

What is best in "French Lessons," though, has to do with Ms. Kaplan's skillful interlocking of memoir and inquiry, her insistent probing into the complex connection between language and self. With a novelist's eye for detail and a critic's acuity, she has given us a rare and moving evocation of what it feels like -- and what it means -- to fall in love with a language not one's own.