GEOFF BENNETT: Well, over the past few weeks, our Judy Woodruff has been speaking to a host of experts about the country's 250th anniversary for her "In Pursuit of Happiness" podcast.

That includes conversations about the role satire, national parks, and music have played in our history, as well as the latest episode looking at how American English has evolved.

As it turns out, there's more than one way that the English language reveals a lot about the way we speak.

I think a really accessible example of how these kind of intrinsic tendencies we have towards change is in the way that we pronounce butter.

VALERIE FRIDLAND, Professor of Linguistics, University of Nevada: So, if you're a British southern British English speaker, a standard Southern British English speaker, you will say something like butter.

(LAUGHTER) VALERIE FRIDLAND: If you're an American, you will say butter.

And there's a natural tendency in language when you have an unstressed syllable because it doesn't get as much attention and love for things to reduce, for sounds to reduce.

And so in British English, especially southern British English, you drop the R. But in American English, we kept the R. So we didn't do that to reduce.

Instead, we reduced with the T. But they start to be imbued with social meaning, so that if you say butter, you're standard southern British.

If you say butter, you're American.

And so you see a difference between social status in Britain, where it's not geographic distance, but it's social distance.

And then you see geographic distance that separated people, leading to the difference between the butter and the butter pronunciation.

JUDY WOODRUFF: You know, I'm listening to the two of you.

I have so many, so many other questions, and I'm thinking about how much Americans move around now.

You may be born in the North, but you move to the South, and vice versa, born in the East, move to the West.

Of course, media, movies, television, radio, listening to other voices, what kinds of -- how has all that, and especially the media, the presence of the media, begun to change, or has it changed, or is it changing how people talk?

ANNE CURZAN, Linguist, University of Michigan: There are the changes and things that people really notice.

So, new slang comes out and everybody wants to talk about six, seven or rizz or what -- these sorts of things.

But one of the things that I study is the more subtle changes that are still happening that tend to go below the radar.

So they're the sorts of vowel changes that I was talking about.

But, for example, I think some people have noticed that the word shall is not healthy.

It is dying out of the language.

What many people have not noticed is that the word must, in the sense of obligation, like I must run errands -- and you can you can hear I do it very seriously, I must run errands.

Because what I would tend to say is, I have to run errands or I need to run errands.

JUDY WOODRUFF: Or I need to run errands.

ANNE CURZAN: So have to and need to are replacing must in this sense of obligation.

These -- if you hang out with young people, as Fridland does as well, that on accident is coming into the language, and by accident is moving out of the language.

Like, we're getting a prepositional shift there.

GEOFF BENNETT: All six episodes of "In Pursuit of Happiness" are out now.

You can watch them on our PBS News YouTube page or wherever you get your podcasts.