Esperanto was designed to be easy to learn and to lack many of the special cases and "gotchas" present in every natural language.
There are probably many cases where it would be easier for a native of some language to learn a specific similar language (i.e. for a Dutch speaker to learn German, or a Portuguese speaker to learn Spanish), but I would not be surprised if Esperanto minimizes the cost function for the net effort required for all native speakers/all second languages.
- The vocabulary is a big part of the language learning and it is hard to even begin with when the target vocabulary resembles nothing in your original tongues. It can be probably argued that ESL learners can learn Esperanto more quickly, but it still represents only about 1/4 of the total human population.
- Rhotic consonants are particularly hard to pronounce correctly even for many ESL learners, and yet Esperanto retains them.
- Esperanto by itself does not have a word order, but it does have a preferred word order of Subject-Verb-Object which is equally probable as Subject-Object-Verb but much more familiar to Indo-Europeans.
- I think Esperanto, in spite of its original premise, has picked idioms and phrases up as well, as common in every old enough language.
It is now widely accepted that the difference between the native tongue and the target language greatly impacts the learning curve. If Esperanto does succeed, it would not be due to the easiness, because the easiness would be highly subjective.
> - The vocabulary is a big part of the language learning and it is hard to even begin with when the target vocabulary resembles nothing in your original tongues.
While this is true for Esperanto, it is also true for any other language, natural or constructed. And the idea of Esperanto is to reduce the effort learning vocabulary not through familiarity, but by deriving its vocabulary from a minimal set of roots and a system of suffixes. In Esperanto, if you know the word for "big", you automatically know how to say "small", "huge" and "tiny". This is not the case in most natural languages.
Of course Esperanto will be much easier to learn for someone who already speaks some Germanic or Romance language than to anybody else on the planet. But even to a monolingual Chinese (or whatever) speaker, I believe building a working vocabulary in Esperanto is going to take less effort than in English, Spanish or German.
> It can be probably argued that ESL learners can learn Esperanto more quickly, but it still represents only about 1/4 of the total human population.
But far more than 1/4 of the total population of _Europe_, which is the only thing that matters in the context of this discussion.
> In Esperanto, if you know the word for "big", you automatically know how to say "small", "huge" and "tiny". This is not the case in most natural languages.
Oh? I have heard that "granda" means big, "giganta" or "kolosa" means huge and "eta" means tiny... :-)
Of course I know what you want to say. One can derive "malgranda" (non-big, i.e. small), "grandega" (more-big, i.e. huge) or "malgrandega" (tiny) from a single root "granda". But that alone does not explain all other words! For example, the Zamenhof's original dictionary [1] lists both "grand-" and "et-" as root words while "gigant-" or "kolos-" are missing (probably later additions, haven't checked). Why the heck do you need to know both "grand-" and "et-" when one is an antonym to the other? [2]
I'm not an esperantisto and I'm not able to discern the nuance behind all those different words, but I see a sign of the mature language here: once regular, now naturalized. It is not necessarily bad and the artificial origin can still help learning, but I would be rather careful to claim that it is "easier to learn than any naturally evolved language". And that leads to...
> But far more than 1/4 of the total population of _Europe_, which is the only thing that matters in the context of this discussion.
You have said universally, even though you didn't seem to realize it. And even when we concentrate to Europe, the actual number of ESL learners is not too different: 38% [3].
But yeah, most Europeans can speak either Romance, Germanic or Slavic languages [3] that form the Esperanto grammar and vocabulary. Still, in the same census most Europeans seem to be much more interested in ESL than others [4] and it would be very hard to convince them to learn Esperanto instead.
[2] Of course, the answer is that it isn't. "et-" is described as "marque diminution, décroissance" i.e. "marks decrease or reduction" and not strictly an opposite of "grand-". It is therefore a fault of fellow esperantistos to use it as "tiny"! </joke>
There are probably many cases where it would be easier for a native of some language to learn a specific similar language (i.e. for a Dutch speaker to learn German, or a Portuguese speaker to learn Spanish), but I would not be surprised if Esperanto minimizes the cost function for the net effort required for all native speakers/all second languages.