Evidence-based answer · Last updated · How it’s made
When someone already knows a second language (L2) and starts learning a third (L3), that prior L2 doesn't just sit there — it actively shapes how the new language is learned, often more strongly than the person's native language (L1) does. Research shows this "L2 effect" competes with other forces (how similar the languages are structurally, how proficient the learner is in each language, and even how learners subjectively feel about language similarity), and which force wins seems to depend on the specific grammar point, sound, or word being learned rather than one single rule.
Answered for language learning in general. No specific language was set for this question, so the findings are drawn from general second-language research rather than one language’s literature.
Multiple studies find that the second language a person learned, purely because of its status as a non-native language acquired after childhood, tends to influence the third language more than the native language does — this is called the 'L2 Status Factor' or 'foreign language effect'.1,3,7,8,17
In plain terms
Several studies find that structural closeness between languages (called 'typology') can override the L2-status effect — learners lean on whichever prior language, L1 or L2, is grammatically closer to the new language, not necessarily the L2 by default.1,3,12,15,17
In plain terms
Even in children learning a third language, grammatical patterns from their dominant second language transferred into the new language, echoing the L2-status findings seen in adults, suggesting this isn't just an adult phenomenon.4
One study found that instead of typology or L2 status, what mattered most was the cognitive complexity of the grammar rule itself — simpler, more explicit rules were transferred from a different source than more implicit ones, challenging the standard L2-status and typology explanations altogether.5
In plain terms
Learners' subjective sense of how similar their languages are — even when that sense is inaccurate — can shape which language they draw from when producing the L3, sometimes more than the actual, objective similarity between the languages.13,16
In plain terms
Example
Having gone through the experience of learning an L2 appears to boost a learner's 'metalinguistic awareness' — their ability to consciously notice and think about how language works — and this heightened awareness may help when tackling a third language.9,10,14
In plain terms
Across the studies, none of the existing theoretical models (L2 Status Factor, Typological Primacy Model, Cumulative Enhancement Model, and others) fully accounts for the range of results; researchers keep finding cases each model fails to predict, and variation between individual learners is very high.2,5,7,15
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