This question: If a parent talks to their child exclusively in [constructed language], does this language become a natural language? was closed as off topic. However, I think it is relevant -- it is about definition of constructed language vs. natural language.
Proposal: Constructed languages
Area 51 doesn't have to same level of visibility as the regular Q&A for me to check if the question was later edited/improved or if I simply read it wrong. No matter; it looks fine, but I am unable to re-open it once the proposal goes into commitment. I wouldn't worry about it. Scoping issues are generally worked out by the people who actually use the site once it launches.
There will be borderline cases, perhaps. One that comes to mind is the Nicaraguan Sign Languages. It is constructed, in the sence that it was completely built ex nihilo, and it is natural, in the sence that it was not consciously designed.
No, the language is still constructed. The label "constructed language" has to do with how the language was created, not how it is subsequently used. A constructed language is consciously created for an express purpose. It is likely however that should native speakers of a constructed language arise the language would start down the path towards spawning a natural language. Or rather, more likely, several daughter languages which would be considered natural. They would be considered natural because they arose due to the action of natural evolutionary forces on an ancestral language. But all languages start life as dialects, so dialects would have to appear in a constructed language first. As yet, this has never happened and it may be impossible for an unknown reason.
