Why does night fall but never break and day break but never fall？Why are people who ride motorcycles called bikers and people who ride bikes called cyclists？In what other language do people drive in a parkway and park in a driveway？In what other language do they call the third hand on the clock the second hand？

Let's face it： English is a crazy language． There is no egg in an eggplant， neither pine nor apple in a pineapple and no ham in a hamburger． Sweet-meats are candy， while sweetbreads， which aren't sweet， are meat．

We take English for granted． But when we explore its paradoxes （探讨它的矛盾）， we find that quicksand can work slowly， boxing rings are square， public bathrooms have no baths in them．

And why is it that a writer writes， but fingers don't fing， grocers don't groce， and hammers don't ham？ If the plural of tooth is teeth， shouldn't the plural of booth be beeth？ One goose， two geese - so one moose， two meese？

How can a slim chance and a fat chance be the same， while a wise man and a wise guy are opposites？ How can overlook and oversee be opposites， while quite a lot and quite a few are alike？ How can the weather be hot as hell one day and cold as hell the next？

English was invented by people， not computers， and it reflects the creativity of human beings． That's why， when stars are out， they are visible； but when the lights are out， they are invisible． And why， when I wind up my watch， I start it； but when I wind up this essay， I end it．

A crucial period for learning the rules and structure of a language lasts up to around age 17 or 18, say psychologist Joshua Hartshorne of MIT and his colleagues.

Previous research had suggested that grammar-learning ability developed in early childhood before hitting a dead end around age 5. However, Hartshorne’s team reports online in Cognition that people who started learning English as a second language in an English-speaking country by age 10 to 12 ultimately mastered the new tongue as well as folks who had learned English and another language at the same time from birth. Both groups, however, fell somewhat short of the grammatical fluency displayed by English-only speakers. After ages 10 to 12, new-to-English learners reached lower levels of fluency than those who started learning English at younger ages because time ran out when their grammar-absorbing ability fell starting around age 17.

Aiming for a sample of tens of thousands of volunteers, Hartshorne began by contacting friends on Facebook to take an online English grammar quiz, which used a person’s responses to guess his or her native language and dialect (方言) of English. Then volunteers filled out a questionnaire asking where they had lived, languages they had spoken from birth, the age at which they began learning English and the number of years they had lived in an English-speaking country.

In the end, the researchers analyzed responses of 669,498 native and nonnative English speakers. Statistical calculations focused on estimating at what ages people with varying amounts of experience peaking English reached peak grammar ability.

Researchers who study language learning regard the new study as fascinating, but exploratory. According to psycholinguist David Barner of the University of California, San Diego, Hartshorne’s team can’t yet say that language skill develops along a single timeline. Different elements of grammar, such as using correct word order or subjects and verbs that agree with one another, might be learned at different rates, Barner says. It’s also unclear whether the responses of volunteers to an online, 132-item grammar test reflect how well of poorly they actually speak English, he says.

What’s more, language learning involves more than a crucial period for acquiring grammar, cautions linguist David Birdsong of the University of Texas at Austin. For instance, growing up speaking two languages at once puts still poorly understood burdens on the ability to grasp grammar, he says.

In the new study, people who were bilinguals from birth fell short of peak English grammar scores achieved by English-only speakers. That’s consistent with evidence that bilinguals cannot easily turn off one language while speaking another, Birdsong says. Interactions between tongues spoken by one person may slightly depress how much can be learned about both languages, even if bilingual communication still reaches high levels, he suggests.

Language diversity is dying. While there are over 5,000 languages in the world, experts estimate (估计)that many are on their way out. Statista, a data provider, compiled(编译)the results of the ongoing work of the Endangered Languages Project to create a map of endangered languages highlighting what regions of the world are most affected.

The Endangered Language Project is an online platform administered by the University of Hawaii Manoa that collects information on the world’s languages, such as where each is spoken, the number of speakers left, what measures have been taken to preserve it, etc. For example, by perusing the Endangered Language Project’s website you can see that Irish Gaelic is an endangered language mostly spoken in Ireland and that consists of four different dialects; Irish Gaelic is spoken by 20,000 to 40,000 people worldwide.

Experts acknowledge that the rapid extinction of languages throughout the world is a fact that cannot be denied, but they also explain that it is very difficult to obtain exact numbers when it comes to languages and their extinction. This is because language information is outdated or limited, and it can be different in some cases to distinguish between languages and dialects. The Linguistic Society of America notes that some estimates state that 80 percent of the world’s languages could be gone by the next century as languages like English, Spanish, Portuguese, Chinese and Russian become even more of a majority.

On its website, the Endangered Language Project also features an interactive map of endangered languages that’s color-coded according to each   language’s level of threat. Each language is represented by a colored dot on the map, and clicking the dot will reveal the name of the language and its status. Clicking on the name of the language will lead you to a more detailed information card about the specific language.