Imagine you overhear a person say: That's like so random and another person say: That's very unpredictable. Which person is almost certainly younger and which older? Which one is using “proper” English and which one is using slang? You might feel you could guess the correct answer to both of those questions. But there's another question that's more interesting: why do young people and old people use language so differently in the first place?

Let's consider three basic facts about language:

1. Language is always changing.

2. No one can stop language change – not teachers, not parents, not the prime minister.

3. Age has a huge impact on how a person uses language.

In our culture, young people usually try to set themselves apart from the older generation – through clothing and appearance, preferences in music, and acutely through language. That's because language is a very important symbol of social solidarity. The ways we use language let other people know who we are and where we belong. As teens gain independence and come in contact with a wider circle of friends, they are exposed to an increasingly rich range of new language uses. When these new uses spread among more and more teens, new expressions enter English, and sometimes they even influence English grammar. This is how young people become the driving force behind language change. You might also be interested to know that girls are far more likely to use new features of language than boys are, which means that girls are the primary transmitters of new usages.

Where do the “new” features of language come from? Young people do not create them out of nothing. As we shall see, young people take the materials already available in the language and modify them in new ways. Here's an example. An older person will almost always use the word very when emphasizing something: “That's very fine.” A middle-aged person will be more likely to use really, as in “That's really nice.” And an adolescent today will undoubtedly say, “That's so cool.”