The 'Chinese' Theory: For and Against

[Jorge_Stolfi]

there is very little diglossia in the US.  Examples would be people saying "ain't" and "gotta" in informal contexts but using "isn't" and "got to" or "will" or "must" when writing exactly the same sentences.  It is much more pronounced in other countries.

Just to elaborate on this last point (even though it has no relevance to the VMS), here is an example of diglossia in Brazilian Portuguese:

  English: "There is no more time, we must leave those two things behind"
  Inform: / 'nũ 'tẽj̃ 'majs 'tẽj̃pʊ, ɐ 'ʒẽj̃tʃɪ 'tẽj̃ kɪ lɐɾ'ga 'esɪz 'dojs 'tɾɔsʊ /
  Written: Não há mais tempo, nós temos que largar esses dois objetos.
  Form:   / 'nɐ̃w̃ ˈ'a 'majs 'tẽpu, 'nɔs 'tẽmuz ki lɐɾ'gaɾ 'esiʒ 'dojz ob'ʒetus /

The informal spoken form is what even a well-educated person would say in most everyday situations.  The written form is how anyone who went through high school without cheating would write, in the same situations.  The formal spoken form is what the same person would say in a very formal situation, like giving a speech by reading from a written text.

The lexical differences from informal to formal include replacing /'a'ʒẽj̃tʃɪ/ = "a gente" (literally "the people") for the formal pronoun /'nɔs/ = "nós" ("we"), and the informal / 'tɾɔsʊ / = "troço" (literally "piece", but usually in the sense of "piece of stuff") for the more formal "objeto". 

The grammatical differences include replacing the auxiliary verb "tem" by the formal "há" ("there is"), the inflection of the verb in the 1st person plural ("temos", matching the subject "nós") instead of the 3rd person singular ("tem", matching the subject "a gente"), and restoring the "-s" plural ending ("objetos") that is often dropped in the informal register ("troço" instead of "troços").

The phonetic differences are many (like informal /'nũ/ versus formal /'nɐ̃w̃/, and dropping of the final /-ɾ/ in the informal version of "largar").  But they would vary a lot from region to region.

All the best, --stolfi