"It is generally said that an infant can learn any language, but it turns out to be relatively easy to invent languages that many people cannot learn at all. Logical languages
(loglans) have been invented as tools for unambiguously expressing some formal, logical statements, and it turns out that people have a tremendous difficulty learning them. What’s more, these languages require the prior existence of a working natural language before they can be learned even a bit. They have to be explained logically rather than learned by listening. The reason seems to reflect the critical difference between a loglan and a natural language. Loglans express formal concepts while natural languages pilot attention. In a loglan the fundamental challenge is to keep everything unambiguous, and sometimes this procedure requires multiple embeddings that would be impossible in natural speech because they disrupt attention. In natural languages, ambiguity is less of an issue because the context helps keep matters clear. The really important thing is for speakers to make it easy for a listener to follow the thread of what’s being said. Embeddings can only come at certain attentional breakpoints, and too many embeddings leave a listener confused. But, it is possible for some determined learners to become conversational in a loglan. Presumably there are one or two freakish situations right now in which an infant is picking up bits and pieces of a loglan along with some other language. The flexibility of human nature can never be forgotten or dismissed. There is a very wide variety of verbal _expression_ possible: logical, metaphorical, joking, analytical, … I don’t know if there is an upper limit. But it begins with perception and directing attention, which in turn rests on a community"