Language transfer is when the learner is trying to apply rules and forms of the first language into the second language. Transfer is an important factor in language learning at all levels. Learners begin by transferring sounds (phonetic transfer) and meanings (semantic transfer), as well as various rules including word order and pragmatics. Language transfer is also known as L1 interference.
When the relevant unit or structure of both languages is the same, linguistic interference can result in correct language production called positive transfer. The more similar the two languages are the more the learner is aware of the relation between them, the more positive transfer will occur.
Negative transfer occurs when speakers and writers transfer items and structures that are not the same in both languages. The greater the differences between the two languages, the more negative transfer can be expected.