Deinonysus wrote:Esperanto's propaedeudic value needs to be studied more.
Strangely, I only ever hear that word used by Esperantists...
However, I think any further research on this needs to be comparative. We know learning Esperanto makes it easier to learn another language. We know learning any language makes learning subsequent languages easier. The only question that leaves is whether Esperanto is measurably better than natural languages at preparing for later language learning.
I think it's tremendously valuable for any speaker of a Western European language (particularly English, Spanish, and French) who wants to learn how to learn foreign languages, and any speaker of other languages who wants an easy introduction to Western European languages.
Except that Esperanto can be misleading, setting up incorrect intuitions, particularly regarding suffixes.
If we did serious research into propaedeutic auxiliary teaching languages, the natural conclusion would be the invention of a completely new set of auxlangs that embody all the principles of language learning in the most efficient way, with the minimum possible traps to lead people away from natural language. We've learned a heck of a lot about how language works since Esperanto was written. Why a set? Because you wouldn't want to focus on e.g. conjugations to people who are going on to study isolating languages after. Implicit in what Deinonysus says above is the idea that the value of Esperanto as a first language diminishes rapidly the further you are from FIGS.
I consider Esperanto a bit like the programming language BASIC: a well-intentioned endeavour that was flawed from the outset and has been massively outdated by advances in technology since.