The next level up is morphology, the aspect of language that deals with words, or more precisely with morphemes. In morphology, where we get into issues of meaning, is based on this extraordinarily neat trick, described by the French linguist, Ferdinand de Saussure, as the arbitrariness of the sign. The idea is that language works on a principle where anything can connect to anything else. A sign is arbitrary in that sense. So, for instance, the sound, dog, the morpheme, dog, the word, dog, bears no interesting relationship to the creatures that it refers to, those creatures with four legs and a tail that bark. So, there's no way you can tell from the sound of the word or a structure what it refers to. There are some correlations. There are some words that are referred to sound, for instance, do carry some of the meanings. So, the word "grown" kind of sounds like a grown. But those are rare exceptions. The word dog, or table, or microphone, or helmet, don't sound anything like the things that they refer to. So, this makes it possible for languages to refer to an infinity of different things, an indefinite number of different things through the arbitrariness of the sign. Now, I'm kind of blurring together right now words and morphemes. The field of linguistics that studies is not called wordology, its called morphology. So, what's the difference? Well, a morpheme is the smallest meaningful unit. It's the smallest thing. Its the most basic thing you have to learn. You can't infer the meaning of a morpheme, it's arbitrary and you have to learn it. This is different from a word because you can combine morphemes to make words. So, can you actually can understand certain words even if you've never heard them before. So, take as an example dog and complain. Those are single morphemes. Complain as more than one syllable, which is a phonological fact about it, but it's a single morpheme. You have to learn what complain means. But now, compare dogs and complain. Now, dogs and complain are each single words, but actually, you don't have to have heard them before to know what they mean. If you know the word dog, and you know the morpheme-s, which means plural, you could figure out that dogs refers to more than one dog. If you know complain, and then you know the morpheme-ed, which means occurred in the past, you know that complained, even if you've never heard it before refers to complaining in the past. So, just as we'll see syntaxes generative, allowing us to understand sentences and phrases we never heard before. Words are also generative, and that morphemes can combine together to create words we've never heard before. This isn't such a big deal for language like English, but it shows up more in other languages like German or Hebrew, which are more productive in how words can be formed. In fact, there are some languages where morphology, combining morphemes into words, there's a lot of work that syntax does for a language like English. Now, one question which always comes up is, how many words do we know? Now we can refine the question somewhat differently, how many morphemes do we know? How many morphemes does a English speaker on average know? It turns out it's very difficult to tell, because a lot depends on how you define what it is to know a word. Estimates are all over the place, but the estimates I trust the most use methods where you take a sample of English words or random sample from a dictionary, and then you quiz people on this random sample, suppose you have 1,000 of them, and then you see how many they know, maybe through a multiple choice test. Then if the sample was one percent of the dictionary, you multiply the number correct by 100, and then you get a reasonable estimate of how many words in that dictionary you're averaging the speaker knows. Again, the numbers are not precise, but it's quite large. By one estimate, your average English speaker knows of it 8,000, and if you do the math, and this is for your average high school graduates, do the math, this means that from the age one, when you start learning words, to age 17, you learned about 10 new words a day. In fact, what really happens is you learn a few new words a day, as a two-year-old, or a three-year-old, but this pace accelerates. Then when you learn to read, you know an extraordinary amount of words. If you just think about words that I'm throwing at you, and I throw some more at you, like apostle, and transmitter, and shoe shine, and beach, valley, I'm just free associating here, but there's a lot of words out there, and we know them, and in a fraction of a second we can retrieve their meaning. So, morphology, or words, or meanings of words, reflects another extraordinary capacity that people possess.