Dual Language System Hypothesis

The Dual Language System Hypothesis is a hypothesis related to determine how children learn languages. The Dual Language System Hypothesis states that children acquire two different language systems from the beginning stages of language acquisition. Each language has its own semantic memory and the rules do not cross over from one language to the other. This hypothesis does not support the idea that bilingual children move through stages to eventually be able to differentiate the two languages. Instead it assumes that bilingual children have two different languages systems and are able to differentiate from the start of language acquisition.


The Dual Language System Hypothesis is supported through various studies relating to the lexical, syntactic, phonological contents of language. It also can be supported through language content itself.

Lexical System

Each language has a lexical system in which speakers follow the general rules to make utterances in communication. The Dual Language System Hypothesis states that bilinguals are able to have two different systems and they are able to differentiate these systems and are aware which system is related to which language. Quay (1995) suggested that bilinguals were able to have two separate lexical systems at the beginning of language development, which would allow them to distinguish between the two languages. He proved this through an experiment in which he studied a Spanish-English bilingual infant, Manuela, from birth to 22 months (Du,2010,p.134). He would videotape the infant for two half hour sessions every week along with a daily diary record. The two half hours were split up to her different languages. She would speak one half hour with her Spanish-speaking father and the other half hour with her English-speaking grandmother (Du,2010,p.124). He discovered that Manuela had a productive lexicon of 300 words, which consisted on 54 equivalent words (words that had the same meaning in both languages and could be used in the same context) (Du 2010, p.134). Manuela was able to distinguish between the equivalent word pairs and utter the English word when speaking with her grandmother and the Spanish equivalent when speaking with her father. These results show that Manuela was able to distinguish between the two linguistic systems and was able to differentiate which linguistic system should be used with which language.

Syntactic System


Syntactic System of an individual is the order in which an individual utters the subject, verb and object of a sentence. Each language has a specific rule for how a speaker should communicate. Speakers of English are aware that the English language is SVO. An example of this is “The girl caught the ball”. The subject is “the girl”, the verb/action is “caught” and the object is “the ball”. On the other hand, Japanese speakers are aware that the Japanese language is SOV. An example of this (translated to English) would be “The girl the ball caught”. As any English speaker would know, this does not make sense in English. The Dual Language System Hypothesis assumes that the bilingual individual would be able to differentiate between both syntactic systems and would be able to use the correct system for each language with out “mixing” the two (Du 2010, p.134). For example Meisel (2000) performed a study of two French and German bilinguals. The subjects were able to use the current function of the early verb inflection to encode subject verb agreement, which proved that bilingual children would not mix subject verb agreement rules in the two languages (Du 2010, p.135).

Phonological System

Along with the syntax and linguistic features, a language also has a phonological system. The phonological system relates to the sound system related to a specific language. The Dual Language System Hypothesis assumes that yet again there are two different phonological systems, one pertaining to each language of the bilingual individual.

To test this, Paradis (2001) created a study to determine wheather bilingual individuals had two different systems or if they only had one. He used both monolingual speakers and bilingual speakers who spoke English and French. The study used a number of nonsense words that were created according to the phonological constraints in each language. Native speakers of both English and French were present to assist in the study. The study used the idea of word truncation, which refers to the phenomenon that young speakers omit syllables when they are producing polysyllabic or multi-syllabic words (Du 2010, p.135). He had the subjects repeat words spoken by speakers who spoke the language to determine wheather or not a different language system had an impact on the phonology of the other. The results of the study showed that the monolingual and bilingual groups had language sensitive responses according to the phonological rules of French (Du 2010, p.135). The discrepancy is seen in a bilingual speaker when he is speaking English. In some cases, some words were influenced by the phonological rules of the French language, which resulted in mispronunciation. Although this was seen, Paradis still concluded that bilingual children have two different phonological systems. In some cases, one system may have influence on the other but the systems remain separate. The language that is seen as dominant by the speaker will most likely have influence on the other language (Du 2010, p.135).

Language Content


According to the Dual Language System Hypothesis, an individual may be able to differentiate on which language is being spoken by an individuals voice. From there, they would then be able to connect the language with its general rules. For bilingual children under the age of two, they may relate certain languages with certain settings or people. In a study done by Genesee, Boivin and Nicoladis (1996) they wanted to see if they used a stranger would the child be able to differentiate between their two languages. The study would be in support of the Dual Language System Hypothesis if they respond with the same language as the one being uttered by the stranger. The results of the study showed us that bilingual children were able to identify the language based on the characteristics of the language and could then respond in the correct language with the correct general rules (Du 2010, p.135). This showed us that bilingual children under the age of two could differentiate the language being heard and respond with the correct language, which supports the idea that children have two different language systems.