L1 interference

L1 interference — also called negative transfer — happens when rules from your first language (L1) leak into your second language (L2). It is the umbrella mechanism behind most systematic ESL errors: false cognates (single words with imported meanings), calques (phrases translated word-for-word), dropped or extra articles, misplaced prepositions, and sentence rhythms that follow your L1's word order.

The key word is systematic, not random. Interference errors follow the grammar you already know. Ukrainian and Russian have no articles, so their speakers reliably write:

Wrong: I sent report to manager yesterday. Right: I sent the report to my manager yesterday.

A Spanish speaker rarely makes that error — but will write I have 30 years (tengo 30 años). Each L1 leaves its own predictable fingerprint in English.

That predictability is good news. You do not need to fix "your English" in general; you need to learn the specific collision points between your language pair. A writer who knows their own transfer patterns can self-edit faster than any general grammar course can teach them.

Interference also matters for AI detection. L2 writers often compensate by writing more carefully and uniformly — shorter sentences, safer vocabulary, less variation — and detectors read that uniformity as machine-like. A Stanford study (Liang et al., published in Patterns, 2023) found AI detectors falsely flagged 61% of TOEFL essays by non-native English speakers. The irony: the traces of interference that make your writing imperfect are also evidence that a human wrote it.