Like many words, "smart" has lots of meanings.

For example, "smart" can describe a well-dressed person. We can also use "smart" as a verb, meaning "to feel pain". But the most usual meaning of "smart" is "to be very good at learning and understanding things". So when students do well at school and get good grades, we say they are smart.

Being smart, however, goes out of classrooms. People can be smart in different ways. If they have been in school for many years and have learned a lot, people might call them "book-smart". Such people often know the names of great thinkers, scientists and other famous people in history. They know facts and information that other people don't know. However, sometimes such people are not smart when it comes to life skills. Then, people who are good at solving problems are "street-smart". They may not have read many books, but they have the ability to use their experiences.

Then, it may surprise you that "getting smart" is not good. "Getting smart” means "being rude or impolite". It is very common to hear parents say to their children, "Don't get smart with me". And that's not the only "smart" expression that can get you into trouble. We often use "smart" with "off" together. In class, there is a student who has a really smart mouth. He gives the teacher smart answers in class too many times, the teachers may say, "do not smart off in class!"

“How are you?” is a nice question. It’s a friendly way that people in the United States greet each other. But “How are you?” is also a very unusual question. It’s a question that often doesn’t have an answer. The person who asks “How are you?” hopes to hear the answer “Fine”, even if the person’s friend isn’t fine. The reason is that “How are you?” isn’t really a question and “Fine.” isn’t really an answer. They are simply other ways of saying “Hello” or “Hi”.

Sometimes, people also don’t say exactly what they mean. For example, when someone asks “Do you agree?” the other person might be thinking, “No, I disagree. I think you’re wrong.” But it isn’t very polite to disagree so strongly, so the other person might say “I’m not so sure.” It’s a nicer way to say that you don’t agree with someone.

People also don’t say exactly what they are thinking when they finish talking with other people. For example, many talks over the phone finish when one person says “I have to go now.” Often, the person who wants to hang up gives an excuse, “Someone’s at the door.” “Something is burning on the stove.” The excuse might be real, or it might not. Perhaps the person who wants to hang up simply doesn’t want to talk any more, but it isn’t polite to say that. The excuse is more polite, and it doesn’t hurt the other person.

Whether they are greeting each other, talking about an idea, or finishing a talk, people often don’t say exactly what they are thinking. It’s an important way that people try to be nice to each other, and it’s part of the game of language.

One day, I happened to meet an Englishman in a store and soon we began to talk. As I was talking about how I was studying English, the foreigner seemed to be very surprised, gently shaking his head and saying, “You don’t say! You don’t say!” I was puzzled（困惑的）, and I thought, “Perhaps this is not a right thing to talk about.” So I said to him, “Well, shall we talk about the Great Wall? Have you ever been there?”

“Certainly. When I’m back home, everyone will laugh at me if I leave here without seeing it. The Great Wall is wonderful!” he answered.

“Yes, it is one of the wonders in the world. And people from all over the world have come to visit it,” I added. As I was telling him more about it, he said again, “You don’t say!”

I couldn’t help asking, “Why do you ask me not to talk about it?”

“Well, I didn’t ask you to do so,” he answered, greatly surprised.

“Didn’t you say ‘You don’t say!’?” I asked again.

Hearing this, the foreigner laughed loudly. He began to explain. “‘You don’t say!’ means ‘Really?’. Perhaps you know little about English idioms（习惯用语）.”

Wow! How foolish I was! Since then I have been careful with English idioms.