One of the great joys of raising children is watching them learn what the world is about with no context to begin with. The acquisition of language is a very complex task for which they must integrate observation and experience, experimentation and feedback, with some assumptions and leaps of faith thrown in as well. One of the first words a child learns is "hi" and it's a delight to hear and know that he understands its meaning.
When you look under the hood, the process of learning this one word entails more than you might think. Babies learn the proper context for "hi," in that it is used when you first see someone you know. It is a greeting, which is a specific kind of action. While adults only use it for people, children will often greet inanimate objects, possibly as practice, or possibly because of a funny quirk in our language in which we greet a chair- you know, the high chair. The ways that children get language wrong tells us about their learning process, because if you look hard enough, you can see that they are using language rules; they just haven't got them down yet. Read about the magic that goes on behind learning the word "hi" at MIT Press. -via Real Clear Science
(Image credit: Andrew Bardwell)