英语是有重音和吞音的语言

Say this sentence aloud and count how many seconds it takes.
首先请大声朗读下面这个句子，算算花了几秒。

The beautiful Mountain appeared transfixed in the distance.

Time required? Probably about 5 seconds. Now, try speaking this sentence aloud.
需要多长时间？差不多5秒。现在，大声朗读下面这个句子：

He can come on Sundays as long as he doesn't have to do any homework in the evening.

Time required? Probably about 5 seconds.
需要多长时间？也就5秒。

Wait a minute the first sentence is much shorter than the second sentence!
等等等等，第一个句子比第二个短好多啊！两个句子放到一起比比看：

The beautiful Mountain appeared transfixed in the distance.
He can come on Sundays as long as he doesn't have to do any homework in the evening.

You are only partially right!
你说对了一半。

This simple exercise makes a very important point about how we speak and use English. Namely, English is considered a stressed language while many other languages are considered syllabic. What does that mean? It means that, in English, we give stress to certain words while other words are quickly spoken (some students say eaten!). In other languages, such as French or Italian, each syllable receives equal importance (there is stress, but each syllable has its own length).
这个简单的练习体现了我们说英语非常重要的一个问题，就是，和其他音节语言不同，英语一种重音语言。这是什么意思呢？意思就是说，在英语中，我们会重点强调特定的词，而其他的词就说的很快，有的学生说是吞音了。其他语言中，比如法语或者意大利语，每个音节都是同等重要的，他们也有重音，但是每个音节的长度是固定的。

Many speakers of syllabic languages don't understand why we quickly speak, or swallow, a number of words in a sentence. In syllabic languages each syllable has equal importance, and therefore equal time is needed. English however, spends more time on specific stressed words while quickly gliding over the other, less important, words.
很多说音节语言的人不明白为什么我们能把英语说的这么快或者吞掉这么多音，因为音节语言中每个音节都是同等重要的。英语是突出强调重要的词，剩下的不太重要的词就带过了。

灵指神探示范can和can't的差别

Let's look at a simple example: the modal verb "can". When we use the positive form of "can" we quickly glide over the can and it is hardly pronounced.
举个简单的例子，我们用肯定式的"can"的时候，会很简单的滑过这个词，"can"几乎不发音。

They can come on Friday . (stressed words underlined)
他们周五能来。（有下划线的单词应该重读。）

On the other hand, when we use the negative form "can't" we tend to stress the fact that it is the negative form by also stressing "can't".
而当我们用否定的"can't"的时候，我们会加强否定语气。于是重读的单词就变成了：

They can't come on Friday .
他们周五不能来。

As you can see from the above example the sentence, "They can't come on Friday" is longer than "They can come on Friday" because both the modal "can't" and the verb "come" are stressed.
所以大家就知道，上面的例句中，"They can't come on Friday"说起来就比"They can come on Friday"要长了。因为"can't"和"come"都重读了。

重读规律帮你说地道英语

So, what does this mean for my speaking skills?
那么，这对我们说英语来说意味着什么呢？

Well, first of all, you need to understand which words we generally stress and which we do not stress. Basically, stress words are considered CONTENT WORDS such as
首先，你需要知道什么样的词通常会重读什么样的词不重读。基本上重读的都是有实际意义的词，如

* Nouns e.g. kitchen, Peter
　　　名词。 例如：kitchen, Peter
* (most) principal verbs e.g. visit, construct
　　　大部分重要的动词，例如：visit, construct
* Adjectives e.g. beautiful, interesting
　　　形容词，例如：beautiful, interesting
* Adverbs e.g. often, carefully
　　　副词，比如often, carefully

Non-stressed words are considered FUNCTION WORDS such as
不重读通常都是功能性的词，如：

* Determiners e.g. the, a, some, a few
　　　限定词，比如the, a, some, a few
* Auxiliary verbs e.g. don't, am, can, were
　　　助动词，如don't, am, can, were
* Prepositions e.g. before, next to, opposite
　　　前置词，如before, next to, opposite
* Conjunctions e.g. but, while, as
　　　连词，如but, while, as
* Pronouns e.g. they, she, us
　　　代词，如they, she, us

Let's return to the beginning example to demonstrate how this affects speech.
现在让我们回到开始的例子来看看这些是怎么影响我们说话的。

The beautiful Mountain appeared transfixed in the distance . (14 syllables)
He can come on Sundays as long as he doesn't have to do any homework in the evening . (22 syllables)

第一个句子有14个音节，第二个句子有22个音节。

Even though the second sentence is approximately 30% longer than the first, the sentences take the same time to speak. This is because there are 5 stressed words in each sentence. From this example, you can see that you needn't worry about pronouncing every word clearly to be understood (we native speakers certainly don't). You should however, concentrate on pronouncing the stressed words clearly.
即使第二个句子比第一个长了差不多30%，两个句子说出来用的时间都是差不多的，这是因为他们都有5个重读的词（划线的部分）。从这个例子中，大家就可以看出你不见的要把每个词都清晰的说出来（我们英语母语的人从来不这么说）。你应该把注意力放在应该重读的词上，把这些词说清楚。