What Is Fossilization?

Fossilization is the term for errors or non-native features that become fixed in a learner's second language and stop improving, even though the learner keeps using the language, hearing correct models and sometimes being corrected. A fluent speaker who has lived abroad for decades but still says "he don't" or "I am here since 2010" is showing fossilized forms.

Origin: Selinker and interlanguage (1972)

The concept comes from Larry Selinker's influential 1972 article "Interlanguage" in the International Review of Applied Linguistics. Selinker argued that learners build a separate, rule-governed system, an interlanguage, which sits between their first language and the target language and develops over time. He observed that most adult learners never reach native-like competence, and that some interlanguage features tend to remain no matter how much exposure or instruction the learner receives. He called these features fossilizable.

Later work, especially ZhaoHong Han's Fossilization in Adult Second Language Acquisition (2004), reviewed the evidence and causes. Michael Long (2003) and others argued that the more cautious term stabilization is often more accurate, because it is very hard to prove that a feature will never change.

Examples of fossilized errors

Why fossilization happens

• L1 interference. Patterns from the first language that feel natural are hard to notice as errors.
• Communication succeeds anyway. If listeners understand, there is little pressure to change.
• Lack of feedback. Adults in workplaces and friendships are rarely corrected.
• Automatization. Forms used thousands of times become fast, automatic habits.
• Reduced attention to form. Once a learner is fluent, they focus on meaning and stop noticing detail.
• Age and motivation are also discussed as factors, though their roles are debated.

Why it matters for vocabulary

Fossilization is usually discussed for grammar and pronunciation, but vocabulary is affected too. Wrong collocations ("do a mistake"), misused false friends and over-reliance on a small set of familiar words can all settle into habit. Many advanced learners understand thousands of words they never use, because their speech has settled into a comfortable but limited productive vocabulary. Pushing new words into active use is one of the most effective ways past this plateau.

How to prevent or reverse fossilization

1. Find your recurring errors. Record yourself speaking or ask a teacher to list errors that appear repeatedly.
2. Target a few at a time. Pick two or three forms and practice the correct version deliberately in writing and speech.
3. Ask for feedback. Tell colleagues or a tutor which specific errors you want them to point out.
4. Notice in input. While reading, pay attention to how native writers express the same idea; save useful phrases and review them.
5. Stretch your active vocabulary. Practice using new words in sentences rather than only recognizing them. See how to expand vocabulary as an adult.

Criticism of the concept

Fossilization is difficult to study because it implies permanence, and no study can follow learners for a lifetime. Errors also vary by context: a learner may produce a form correctly in careful writing but not in rapid speech, which makes it hard to call the error fixed. For these reasons many researchers use fossilization descriptively and treat it as a strong tendency rather than an absolute end point. For learners, the practical message is encouraging: persistent errors can usually be improved with focused attention.

Sources: Selinker, L. (1972) Interlanguage, International Review of Applied Linguistics; Han, Z. (2004) Fossilization in Adult Second Language Acquisition; Long, M. (2003) Stabilization and fossilization in interlanguage development, in The Handbook of Second Language Acquisition.