“He felt that since he couldn’t do it, the rest couldn’t do it,” said Prof. Lee Cher Leng, a language historian in the China studies department at the National University of Singapore, referring to Mr. Lee’s inability to fluently speak multiple languages. “He felt it would be too confusing for kids to learn the dialects.”

As the government considered which of Singapore’s many languages to focus on, Mandarin Chinese and English were the logical choices. China, although more than a thousand miles away, was the ancestral homeland of most Singaporeans and was embarking on economic reforms that captivated Mr. Lee. English, the language of Singapore’s elite since the British established a trading port here in 1819, was the dominant global language of culture and commerce.

But neither language had much to do with the people who lived in Singapore when the government launched its policy in the 1970s.

Then, as now, roughly 7 percent of Singaporeans came from southern India and most spoke Tamil. Another 15 percent spoke Malay. The ethnic Chinese, who then as now make up 75 percent of the population, had immigrated over the centuries from several mostly southern Chinese provinces, especially Fujian (where Hokkien is spoken) and Guangdong (home to Cantonese, Teochew, and Hakka). Only 2 percent spoke Mandarin.

Although called “dialects” by the government, some of these Chinese tongues are at least as different as the various Romance languages. The government’s policy was something like ordering Spaniards, French and Italians to abandon the languages they grew up with in favor of Portuguese.

The policy was rolled out in waves. In 1979, the government launched a “Speak Mandarin” campaign. In some schools, pupils who spoke dialects were fined and made to write out hundreds of times, “I will not speak dialects.” The population was bombarded with messages that dialect speakers had no future.