Languages are hard cultural elements because they are complex systems of representation that take a long time to learn and rely on a high degree of uniformity to work. Language occupies a significant portion of the brain’s stored memory, and research indicates that it is most efficiently and effectively learned before one is twelve years old. Even good speakers who learn a language after twelve store the new language in a different way in the brain than those who learn it earlier, suggesting that language acquisition is more complex than learning many other skills. Furthermore, learning a new language later in life is difficult and rarely completely mastered. Even though most people are capable of learning new languages even when they are quite old, they are unlikely to speak the new languages with native levels of proficiency. Language change rarely takes place, therefore, within one generation, for the effort of replacement is very large and not very productive. People may learn a new language and speak it every day, but they are unlikely to forget their original language, and in most cases will revert to it when circumstances permit.

Language change takes place, rather, between generations, when children are acquiring their language for the first time. Children can acquire more than one language at a time and still achieve native levels of proficiency, so it is possible for children in a multilingual setting to become multilingual themselves and communicate freely in both or even more languages. If there are strong pressures to speak just one of the several languages, however, they may abandon their own multilingualism with their children, thus making a new generation that is monolingual. A model of three-generation complete change (immigrant speakers of one language, bilingual children, and monolingual grandchildren in a different language) thus makes sense, and is widely observed in immigrant communities in modern days.