REVISED JOURNAL ENTRY 4
REFLECTING ON LENNEBERG’S CRITICAL PERIOD HYPOTHESIS
11 June 2025
Reading about Eric Lenneberg’s Critical Period Hypothesis (CPH) made me reflect deeply on how we learn language. Lenneberg argued that there is a “window” in childhood, ending around puberty, when our brains are especially primed to acquire language, or well, most things — especially language— more naturally. His theory was based on observations of children with brain injuries: those injured before puberty often recovered language skills better than those injured later. This makes sense—our brains are more flexible when we’re young.
The tragic case of Genie, a girl isolated until age 13, strongly supports this theory. Despite receiving help after being rescued, she struggled especially with grammar, as if her brain had missed the most critical time to learn. It’s heartbreaking, but it powerfully illustrates how essential early exposure to language is.
However, not all researchers agree. Some argue that adults can still learn languages, just in different ways. Maybe the “critical period” isn’t a strict deadline but more of a gradually fading ability. Of course, we can’t compare a typical adult learning a second language to someone like Genie, who never acquired even a first language, despite having the potential. She had missed the window, and afterward, it seemed impossible for her to fully grasp how communication and language work.
Her case illustrates several important theories. It shows how crucial exposure is for language development, supports the existence of a critical period, and perhaps most importantly, reminds us that humans are inherently social beings who need interaction to grow and learn.
The Critical Period Hypothesis also carries important implications for education. If children learn most effectively at a young age, some might argue that language education should be emphasized early. But it’s not that simple. Learning a language in a school environment — an artificial setting — is not the same as acquiring a first language naturally at home.
Parents may not speak the language their child is learning at school, which makes reinforcement at home difficult. And school instruction alone often isn’t sufficient — unless the school is fully bilingual, where students use the second language not just in language classes (like Spanish or German) but also across subjects like maths, history, and science.
This makes me wonder: Is the Critical Period Hypothesis only about first languages? Lenneberg focused on that, but later studies, like those by Birdsong, suggest that second languages might follow different rules. Perhaps our brains adapt as we age, but don’t fully “close the door” to new languages.
When I studied this topic with my friend and professor Isabella Mozzillo, she pointed out that several factors can either help or hinder the language learning process. Is the person motivated? Do they like the language they’re learning? These questions matter.
Take, for example, an immigrant who was forced to leave their home country and must now learn a new language out of necessity, not choice. This emotional burden can act as a major block to learning. On the other hand, if the new language is associated with positive memories or aspirations, it can actually help the learning process.
We also have to remember that some people are naturally inclined to learn languages, while others may have different strengths. There are many variables at play in language acquisition, and the Critical Period Hypothesis doesn’t account for all of them, especially when it comes to learning a second language.
Overall, Lenneberg’s work reminds me that language learning is not just about practice — it’s also closely tied to biology. But the ongoing debates show that we haven’t yet figured out exactly how it all works, especially in second language acquisition. Personally, I don’t see the Critical Period as a strict cut-off point, but rather as a phase where language learning is easier and more intuitive. After that, it’s still possible — just different. This uncertainty is exactly what draws me to linguistics: unlike fixed equations, language is dynamic, complex, and always open to interpretation.
