Hi Christina
You asked
> Why is it not possible to be precise about the number of languages
that
> exist in the world today (about 4000)? Could anyone tell me which is
> more likely--that the number of languages spoken will be smaller or
> larger in the future?
People can be fairly specific because of the amount of linguistic work
that has been done for a century. And then they make some judgement
calls. For example, in Papua New Guinea a linguist proposed that there
were (on the basis of a survey kept by the Summer Institute of
Linguistics at Ukarumpa) that there were 736 languages in the country.
This has been widely quoted, and used to help build up the numbers you
mention.
But I know from the Southern Highlands of Papua New Guinea, for
instance, that there is a chain of languages, from Anggal Heneng in the
North West in Nipa, through various dialects in the Lai Valley and
Mendi, to Kewa in Kagua and Erave, through various dialects to
Samberigi. Now is this three languages with seven dialects, four
languages with four dialects, one language with eleven dialects, or
eleven languages. It's a judgement call... Clearly Samberigi speakers
cannot understand Nipa Anggal Heneng speakers. But they have a fair
chance at working out what Erave Kewa speakers are saying. Thus 4,000
languages - 5,000 languages? Who knows?
Regarding the increase or decrease in the languages of the world -
there are forces both ways. Some forces tend to reduce the number of
languages (eg. the globalisation of cultures, institution of national
systems of education etc), other forces tend to fragment languages
(spreading of languages widely across groups which don't have a great
deal of intercommunication, reductions in transport between areas etc).
At the moment it is clear that the forces that reduce languages
clearly outweigh the forces that increase languages. So we are in a
world in which the number of languages is falling - and probably
falling very fast.
Hope this helps
Warmest regards (and thanks for your post)
John