Which International Auxilliary Language (IAL) should you learn?

I'm going to take a risk here.  I'm going to risk telling you about the fact there there exists not just one "international language", but several, developed by different groups of people.  By telling you this, I risk making you feel uncomfortable about deciding which language to learn.  "After all", you might naturally think to yourself, "if I learn one of them, I won't be able to understand what is written in the others".  I also risk making you mock the very idea of an international second language for everyone.  After all, what's the point of everyone learning an "international language" if everyone learns a different one!

However, I want to calm your fears.  First of all, as I will try to explain, it appears that out of all the constructed languages, only two of them are serious contenders for the title of "THE international language".  Secondly, all noteworthy "international language" projects have chosen word roots from the European family of languages.  Some projects have been biased toward similarity to Latin, others toward English, but for the most part, vocabulary has been chosen according to this principal:

    "The best international language is the easiest language for the greatest number of people"

This is a bit vague, but you get the idea: It's better to choose a root that half a billion people know than one known to a mere hundred million.  This principal naturally leads to arguments such as...

1. Latin is a poor choice for root selection because it is a dead language.  Simply picking latin word roots, without any regard for modern languages, makes an IAL unnecessarily difficult.  This seems obvious to me, but since there have been several Latin-based projects, it is obviously not obvious to everyone.

2. English is an extremely popular language, but if you choose roots from English while ignoring other languages, you'll end up with a huge number of words that are completely unrecognizable by those who don't speak it.  Choosing English roots means you'll have words recognizable by up to four hundred million people (well, I don't know the exact numbers); but in many cases, it is possible to find roots that closer to a billion can recognise.

There are certainly advantages of biasing root selection toward English; but making the language easy "for the greatest number" is not one of them.

Now, in truth, choosing roots is a difficult process booby-trapped at every turn with pitfalls, so let's talk about it no more.

The point I want to make is that most IAL projects end up choosing very similar collections of word roots, because they all choose their roots according to similar criteria.  This happy fact means that if you learn one IAL, it is much easier to learn a second.  So if you go to the trouble of learning one IAL, and if that IAL should end up in the wastebasket of history, don't feel too bad: you can migrate to another using, let's say, half the time it took to learn the first.  Ido and Esperanto are particularly similar, since Ido is the "offspring" of Esperanto.

What languages are there?

As an amateur writer, I tend to take the liberty of writing about my subject before thoroughly learning about it.  So I don't know very much about most of the constructed languages, and have learned a significant amount about only three languages: Esperanto, Ido, and Novial.  It looks to me like Novial might be the best of the three, except that it was designed by only one person and has been learned by very, very few people and hence is not fully developed.

If you want a fairly detailed overview and history of IALs, go here.

I will now summarize some keys points about the modern IALs that are generally considered noteworthy.  Presumably there have been more IAL projects since the 1950's, but for whatever reason, they rarely get any attention.

Of these languages, I think that if any IAL ever becomes truly popular in the world, it will most likely be Ido or Esperanto.  The main reason for this is that Esperanto has more adherents than all other IALs combined, and hence most IAL propaganda (you know, the kind of propaganda which promotes good ideas, not the Nazi kind) promotes Esperanto.  Ido's advantage, then, is its similarity to Esperanto, which
  1. Tends to encourage those who are learning or have learned Esperanto to learn Ido in addition, or instead.  Some of those who do that will "defect" to Ido.
  2. Allows one to consider Ido as a path to learning Esperanto.  Since Ido has easier grammar than Esperanto (mainly, no plural adjectives and few mandatory accusatives), one can learn it first without worrying as much about grammar, and thereby acquire a knowledge of the international word roots in Ido and the affixes (prefixes and suffixes) that are common to both Esperanto and Ido.  Having learned the vocabulary of Ido, one can then focus on the grammar of Esperanto without worrying as much about vocabulary.  In this way, one can learn both Esperanto and Ido in not much more time than one needs to learn just one of them.  Mind you, even when the vocabulary matches, you'll need to learn about the extra inconsistencies in Esperanto.

Learn Ido or Esperanto.

Or at least spread the IAL idea.  As I've outlined before, language barriers are very expensive (in terms of time and money), and I believe that language barriers are a large cause of inequality in the world.  Therefore, to eliminate language barriers would make the world a much better place.

If the number of speakers of IALs reaches a certain critical mass, then interest in it will explode.  It's called the network effect.  Consider the telephone.  If only fifty people in a city of 100,000 has a telephone, then the remaining 95,950 people have little interest in getting one because they won't be able to call much of anyone.  That's the state that Esperanto is in right now.  But as the number of telephones increases, the interest in them increases as a result, until eventually they're flying off the shelves.  Pretty soon virtually everyone has a telephone.  The usefulness of a telephone increases almost quadratically with the number of people who have one, and so it is with IALs.

But someone has to buy those first telephones and spend the money needed to install the equipment.  It was necessary that some people did this, otherwise telephones could never become popular.  For the early adopters, they were largely spending more than they got back in value from their equipment.  But those early adopters were what made possible the expansion of the telephone until it was in every household.

Likewise, the IAL movement needs pioneers, and every new speaker helps a little bit.  It may seem like you're spending more time than the benefits justify.  But if you live long enough to see the day when your IAL is ubiquitous, you'll have to concede that it was worth it.

So which to learn? Ido or Esperanto?

Disadvantages of both Ido and Esperanto
Problems of Esperanto (where Ido improves)
Problems of Ido (compared to Esperanto)