is theory assumes that the two languages are separated in the human brain without any interaction which proved to be untrue.
According to Baker (2011)'' the evidence suggested the opposite'', the languages are not separated in the human brain and the languages interacts and there is a transferring from a language to another. The example he gave for his argument is in the school lessons where the lessons in English they do not feed the English part of the brain only, or if the lessons are in other languages, for example, Spanish the data won't be transferred to the Spanish part only . The data learned in one of the languages can be simply transferred in the brain to the other part, so in this case a concept learned in English can be used immediately in Spanish. This idea of the of bilingualism is called Common Underlying Proficiency (Cummins, 1980, 1981) It is explained as the Iceberg Theory, where the two languages takes a part in the brain seeming to operate separately like two icebergs on a surface, but underneath the surface the icebergs melts into one direction which is the central operating system where both languages interacts an function through the same central operating system (Ibid). The main point in the Iceberg theory is the shared function of the two languages depending on one main source, which puts the two languages on the same level of sufficiency. But this is not a general bilingual law, there are many bilingual people who tend to use one of the two languages more often because they are more capable of expressing their thoughts or feelings in one of the two languages more than the other language , despite they master both languages.
The Separate Underlying Proficiency model and the Common Underlying Proficiency model of bilingualism do not give a definite idea about the function of the brain and bilingualism, and each person's brain analyze the income information and translate it to language in a different way, and most of the researches in the field of bilingualism tried to figure how does the human brain deal with language, these researches target was to have a clear approach to achieve balanced bilingualism. Therefore another theory aimed to reach an approach the relationship between cognition and level of bilingualism, this theory in known as the Thresholds Theory and it was first presented in 1976 and 1977 by Cummins, Toukomaa and Kangas , this theory explained the bilingualism as two threshold each one is a level of language that'' has consequences for a child'' (Baker,2011). The first threshold for a child is to avoid the negative consequences of bilingualism , which might be confusion of language and balancing between two languages. The second level is to obtain the positive benefits of bilingualism (Ibid). This second threshold is when the child gains the social and educational skills to benefit of the aspects of being bilingual, this skills are the main step to achieve bilingual balance when a child learns to benefit from the two languages to the maximum limit in supporting his/her developmental process. This idea gives a reasonable approach to the child bilingual ability and how he/she learn to adjust this ability to improve their lives and use it as a tool in their development process. Meanwhile Dodson (1978) presented his view on bilingualism from a different perspective. He argued that ''a child's mind is focused mainly on the language itself.'' In message- oriented communication, the child's aim is to communicate a message which is not about language, so that language becomes the tool rather than the focus of attention''.( Daniel ,2002) ''He then proposes that the latter should be an integral part of every second language activity unit at the infant and junior school levels'' (Dodson, 1978). In Dodson's theory the language is just a tool that the child learn to benefit from it to develop in all ways, instead of focusing on developing the child's language ability itself .
6- Bilingualism and Ideology
Bilingualism and Civic ideology: ''It expects language minorities to adopt the public value