If you speak English, why bother learning a second language? After all, English is spoken in most countries now, and it's spreading. You don't need French to order a sandwich in Paris, not anymore.

But learning a second language isn't merely about ordering a meal in a foreign country. It's about perspective. Every language is a lens. If you were born wearing pink glasses and could never take them off or exchange them for another shade, you would assume the world is pink without even being aware of pinkness as a quality--pink as compared to what? In the same way, if you know only one language, it's hard to be aware that you are looking through a lens: You think you are simply seeing the world as it is. Fluency in a second tongue gives you a chance to see through a different lens. That can help you realize that some part of what you are seeing is not the world, but the lens--even when you go back to your original language.

Last summer, I was in Colorado with a bunch of my Afghan cousins, sitting on a lawn and lazing away the summer afternoon. As the light sank, one cousin said, "Let's go indoors. I'm getting qukh."

"Well," said my cousin, "you know, how if you sit on grass long enough, especially late in the day, the moisture rising from the earth makes the fabric of your pants damp?"

Yes.

"And you know how the damp fabric clings to your skin?"

Uh-huh.

"And when you pull the fabric away, your skin feels kind of bumpy and itchy?"

Yes.

"Well, that's qukh!"

Now, this usage may seem so precise and limited that one would rarely find a use for it, even if the word existed in English. But the very next day, driving to Aspen, my back was sweating against the vinyl seat; it made the shirt stick to my skin; and after a few hours I had to pull over because--well, I was feeling a bit qukh. Since then, I have noticed ever so many instances of this phenomenon.

Of course, English could adopt this word, or any word, if English speakers found it useful. That's what languages do. But once a word comes into English, it is used in real-life English-language situations, in letters and literature and conversations, and thus accumulates associations that make it an organic part of the experience of English-speaking people. These associations and connections, these capillaries of meaning, seat the word in the living flesh of the English language. And every word in a language has such capillaries connecting it to all the rest of the language. We don't see them but if we know the language, we feel them: They are a part of its meaning.

I suppose it's no use telling you that this couplet thrums with mysterious erotic resonance in Persian. Few English speakers will be convinced, especially about the Eros.

But why is so much lost? After all, practically half the words in this couplet are names. They sound and mean the same in English as in Persian. Samarkand, Bokhara, and Shiraz are cities you will find on any English-language map. And even in English, Turks are Turks and Hindus are Hindus. Some translators fuss with synonyms to inject rhythm and rhyme into the lines, hoping to recapture the music of the original. It's no use. At the end of the day, you're still left with that Turk. And that mole.

And in those same societies, Persians also commanded an authority of their own, based on a supposedly more ancient cultural sophistication. They contributed poetry, art, perfume, an appreciation of gardens--and Shiraz epitomized the romantic Persian city. It was the Venice of the Persian world.

Finally, there's that mole. Westerners don't go for moles. No, no, we just don't. It's no better if they're Hindu moles. No mole at all is the look we prefer. No accounting for taste. Frankly, 30 years ago, I never would have guessed that stylish young American women would one day sport tattoos or that guys would find tattooed women attractive.

In short, to convey any hint of what Hafez was up to in that famous couplet of his, a translator might have to go with something like this:

But would that really count as a translation? Now you've got the capillaries--maybe--but you've lost the word. You see the problem.

And the problem goes beyond vocabulary. A view of the world is embedded in the very structure of a language, any language. Pronouns, for example, have no gender in Farsi. A religious statement never forces or lets you assign a gender to God. In French, by contrast, even bicycles have gender, as do abstract ideas, and their modifiers must conform. What do fluent speakers of this language see? I have trouble imagining.

In Turkish, I am told, the first vowel in a sentence determines what all the other vowels in the sentence will be. Change the first word and the whole sentence sounds different. Hmm.

Tahitian consists almost entirely of separate word parts that stand alone. You need a whole sentence to express all the meanings that English can pack into a single highly inflected compound verb.

A French teacher in Colorado once said to me, "My students keep asking, 'How do you say this or that in French?' And I'm at a loss because the real answer is, 'You don't.'"

Any encounter between two languages involves an intersection between two whole frames of reference. Fluency in a second language cultivates an ability to put oneself in another point of view. Monolingualism makes it more difficult to see that one even has a point of view. Communication, I think, can occur only when both parties are able to imagine the existence of another whole frame of reference. Only then can they approach a conversation as an exploration in which the two parties build a common meaning together--a new and shared frame of reference.

And that is why, in my opinion, the world would be better off if we all knew at least two languages--any two.