​Factors behind language shift
Why is there an inter-generational language shift? As Scotton (2006) says, the contributing factors behind can be systematized into 3 categories. Yet, not all of them play a role in the case of every individual and in every family so it would be interesting to look at the specific factors for individuals in this family.
Societal-level factors
This refers to the factors relating to the outer environment that is hard to be controlled by individuals. These factors often suggest individuals do not get to decide their language uses!
Societal-level demographic factors
The effects of such factors are most reflected in the first generation. After immigration, the Thai mom no longer finds herself living with Thai speakers surrounding her. She does not get much chance to speak Thai as before.
Another reason comes from the concept of vertical and horizontal multilingualism. One is said to be living in the condition of horizontal multilingualism if she is isolated from speakers of other languages in an outer multilingual environment. In contrast, an urban dweller (who is not a NEET!) would more likely need to go out and engage with people from all walks of life speaking different languages. Back to the Thai mother, she only works part-time sometimes when she feels bored. And in the home environment, her husband speaks Thai and acted as an interpreter when there were relatives. There is no urging necessity to deal with Cantonese speakers extensively so she actually could be living in horizontal multilingualism. Yet, she chooses to have Cantonese as a home language and practices it through the home environment. In this sense, she self-constructed a space of vertical multilingualism.
Societal-level occupational factors
When jobs require dealing with Cantonese speakers, one would have to use Cantonese in quite a proportion of time. This is what happens to the two daughters who work full-time and indeed also to the Thai mom who works half-time.This refers to the factors relating to the outer environment that is hard to be controlled by individuals. These factors often suggest individuals do not get to decide their language uses!
Societal-level educational factors
School life occupies a great proportion of a person’s younger life. When Cantonese was used as a medium of instruction, the daughters have already been accustomed to using Cantonese since small.
Individual views and aspirations
Apparently, the opposite of societal factors would be individual factors. In this case, it actually matters a lot to explaining both the Thai mom and the daughters’ current language uses.This refers to the factors relating to the outer environment that is hard to be controlled by individuals. These factors often suggest individuals do not get to decide their language uses!
Because of the mother’s high emphasis on education, which as we mentioned was essentially carried out in Cantonese, she decided to let her daughters learn Cantonese since small and would not risk having Thai confusing them. And to a large extent because of this, she learnt Cantonese together with her small children. That is why she uses Cantonese even at home.
In-group factors
Between the two extremes of societal and individual factors are in-group factors. Cantonese is a very vibrant language in Hong Kong. It has a greater sense of subjective ethnolinguistic vitality compared to Thai. It would be natural that one would lean towards using Cantonese.
An Implication
Some of you may have noticed that these factors do not take effect independently. Instead, they are interactive e.g. a societal-level educational factor can play some role in shaping individual views and aspirations. This also suggests that societal factors and individual factors are not necessarily segregate. Sometimes a language "choice" resulting from individual reasons may not be a choice indeed.
Reference:
Myers-Scotton, C. (2005). Language Maintenance and Shift. In Multiple voices: An introduction to bilingualism. Wiley-Blackwell.