Linguistic Interdependence Hypothesis

The linguistic interdependence hypothesis is a hypothesis about bilingual language development, proposed by the researcher Jim Cummins, which holds that a bilingual person's proficiency in a second language partly depends on the level of proficiency they have already developed in their first language, because certain underlying language-related skills, particularly the more cognitively demanding ones involved in literacy, abstract thinking and problem-solving, transfer across languages rather than having to be built up separately in each one. Cummins illustrated the idea with the common underlying proficiency model, sometimes called the dual iceberg or one balloon model, in which the two languages of a bilingual person appear as separate surface systems, in vocabulary and grammar for example, while below the surface they draw on a single shared pool of cognitive and academic language proficiency; strengthening that shared underlying proficiency through either language, the model implies, benefits both. The hypothesis has been influential in bilingual education policy because it suggests that time spent developing literacy and academic skills in a child's first language is not time taken away from learning a second language, but can instead support the eventual development of similar skills in that second language, an argument used to support continued instruction in a child's home language rather than switching a child into a new language of instruction as early as possible.