Language Transfer is the current term for cross-linguistic influence, i.e. the influence of the mother tongue (L1) on the production of the target language (L2). So, for example, the L1 German learner of L2 English who says
Careful! The glass has a crack! (Vorsicht! Das Glas hat einen Sprung!)
is using both the definite and indefinite article is an identical way to how they would be used in German in such a context. This is an example of positive transfer because the result is grammatical English.
But the same German speaker might ask:
Do you play flute?
since in German no article is used (Spielst du Flöte?), whereas the definite article is needed in English. In this case the result is ungrammatical and the transfer, or cross-linguistic influence, is negative.
It would seem intuitive then that the mistakes learners make in English are the inevitable result of negative transfer (or interference) from the mother tongue. Indeed, this was the strong position taken by early researchers in Contrastive Analysis, the term for the study of cross-language influence. For example, Lado in his Linguistics Across Cultures (1957) hypothesized that:
... those elements which are similar to [the learner's] native language will be simple for him, and those elements that are different will be difficult.
But this is now known to be an overly simplistic theory, which does not account for all of the errors made in the production of the second language.
As Odlin notes in the introduction to his book Language Transfer: Cross-linguistic influence in language learning (Cambridge University Press, 1989) the increasing amount of empirical data about L2 learner errors that was produced in the 1970s called Lado's hypothesis into question. Odlin gives the example of the common omission of the copula (the verb to be) by L1 Spanish speakers of English:
... speakers of Spanish, which like English, has copula verb forms, frequently omit forms such as am or is. Moreover, such errors are not only found among Russian and Spanish speakers, but also among speakers of other languages - and also among children learning English as their native language. Thus, while a contrastive analysis might explain a Russian speaker's omission of copula forms, a Spanish contrastive analysis would not explain the same error as they acquire English. The pervasiveness of certain types of errors has thus been among the most significant counterarguments against the importance of transfer.
Odlin reviews research data that convincingly shows that the presence of a language element in L1 does not guarantee that it will be correctly reproduced in the L2. Conversely, the absence of a language element in L1 does not necessarily mean that it will cause difficulties if it is present in L2.
So the strong position of Contrastive Analysis held by linguists such as Lado is not tenable. Nevertheless, Odlin ultimately comes to the following conclusion:
Despite the counterarguments (to Lado's theory), however, there is a large and growing body of research that indicates that transfer is indeed a very important factor in second language acquisition.
A more recent book which summarizes the results of the research and derives implications for teachers is Learner English: A teacher's guide to interference and other problems (ed. Swan & Smith, Cambridge University Press, 2001). It aims "to help teachers anticipate the characteristic difficulties of learners of English who speak other mother tongues, and to understand how these difficulties arise".
The book is clearly based on the conclusion that Odlin came to, namely that L1 transfer plays a significant (but not exclusive) role in the production of L2. The introduction has the following text, with various references to article use, which is a very common source of errors for certain ESL learners:
There is less disagreement than there used to be about how far interlanguages are influenced by learners' native language, and most linguists would probably now agree that the mother tongue can affect learners' English in several ways:
1. Where the mother tongue has no close equivalent for a feature, learners are likely to have particular problems in the relevant area. Japanese or Russian students, for example, whose languages have no articles, have a great deal of difficulty with English articles.
2. Where the mother tongue does have an equivalent feature, learning English is in general facilitated. French or German-speaking students, for instance, find articles relatively easy in most respects, despite the complexity of the system.
3. However, equivalences are rarely exact, and so-called interference or transfer mistakes are common where students assume a more complete correspondence than exists, so that they carry over mother-tongue patterns in cases where English forms or uses are not in fact parallel. French or German-speaking students typically make certain mistakes in English (e.g. *The life is hard, *My sister is hairdresser) precisely because their languages do have article systems.
Clearly, these findings are of most relevance for ESL teachers as they guide their learners in the acquisition of grammatical English. But the findings can be helpful to mainstream teachers too, particularly those who are proficient in or native speakers of the languages (L1) of the students in their classes. They can predict what language the students need to produce for a particular task and alert them to how the English means of expression is different from the way that the same meaning is conveyed in the student's mother tongue.
For example, Swedish has what is known as a resumptive pronoun which doesn't exist in English. This might lead L1 Swedish students to write definition sentences in science such as:
Chlorophyll is a green pigment which it is found in plants.
Photosynthesis is a process that its source is sunlight.
There is information elsewhere on this website on the differences between English and other major world languages.
More on language errors in written English.