So, let's start at the most basic level. Phonemes are the building blocks of language. Phonology is the branch of linguistics that studies them, studies what phonemes there are, and how they're put together to construct words. English has about 44, I think. As you can tell, since there's only 26 letters in the English written language. Phonemes and letters don't match up one-to-one. In particular, some single letters in English can correspond to multiple phonemes. It turns out there's a universal body of phonemes, and different languages select from them. Interestingly, sign languages of which there are many, work the same way. There are basic units of sign basic primitive movements from which all signs are built from, and different sign languages choose different subsets of these possible movements. Now, when you learn a language, there's a lot that has to be learned. You have to learn what phonemes your language has, and I'll return to this a little bit when I talk about language acquisition. You have to learn the rules and principles through which the phonemes can combine. This helps you know what in your language is a possible word, and what isn't. Most interestingly, at least for me, you have to figure out how to segment speech into words. How to use the principles of your language to figure out where the words are. You might think that's silly, children just start off by learning words and then they learn language as a whole. But the problem is that when you listen to a language right now or as a baby, there are no obvious cues to where one word begins and another one ends. This is hard to tell, because there's an illusion. So, as you hear me speak, it sounds as if there's gaps between the words. But this is an illusion caused by the fact that you already know the words. So, once you know what the words are when people say them in a stream, your mind inserts gaps between them. You could tell that happens because when you hear a sentence in another language, like I hope I get this right, Hebrew, [inaudible] which I think is where's the bathroom or [inaudible] in French. If you don't know these languages, it just sounds like a garble. You get the impression that everybody speaking your language talks normal words with pauses between them, and everybody speaking other languages just garbles incessantly without meaning. So, knowing the words of English, helps you make sense of sentences, makes you tell, where the words are. But of course, the problem for the child, is the child who doesn't yet know the words of English has to learn and in a context, where it's not clear where the words begin and where they end. This is one reason why language learning is so difficult, and it's one reason why phenology, even the most basic aspect of language, poses some very interesting puzzles.