为什么英语要有重音呢？
首先，重音分为两种，sentence stress, word stress。今天我来解释一下为什么有句子重读。
一个sentence 中一般有content words,和structure words. 重读一般发生在content words上。
1. 句子当中的重音，是为了使这个句子好理解，因为重读可以把句子当中重要的成分和不重要的成分区分开来。你用重音去强调部分(stress the most important part)，传递新信息(rather than old),对比信息(contrast)，或者是澄清信息(to clarify)。比如说：will you sell my car becuase I've gone to France.(content words: sell, car, gone, France是被重读的部分。）如果你把structure words部分去掉，句子还是可以大概理解的。无论这句话你说的多么快，只要这四个词清楚，这句话都可以被理解。
2. 句子当中的重音，是为了区分单词的意思。这个好理解REcord, reCORD.以及其他情况。
3.句子的重读，给了语言一种音律美（rhythem）,可以区分语言。每个重读都像是一个beat。听起来好听。而每个语言的rhythm是不同的：中文的京剧（每个音都重读），英文stress-timed language（每个重读之间的时间切分是一样的）。
最后，稍微涉猎一点为什么英文有word stress。首先要知道，日语中文法语都没有word stress，或者简单粗暴的认为，它们的word stress 就在末尾。哒哒哒哒哒哒。每个单词都背同样的被emphasized（理论上，不带有情感的话）。但是在英文中，word stress 有助于说话特别快的时候分清楚说的什么。比如说photograph, 和photography。看一下这个人写的例子“Think again about the two words photograph and photographer. Now imagine that you are speaking to somebody by telephone over a very bad line. You cannot hear clearly. In fact, you hear only the first two syllables of one of these words, photo... Which word is it, photograph or photographer?
Of course, with word stress you will know immediately which word it is because in reality you will hear either...
PHOto... or phoTO... So without hearing the whole word, you probably know what the word is..."
References
https://www.englishclub.com/pronunciation/word-stress-why.htm
https://jimmyesl.com/importance-word-stress/
https://www.google.com.hk/search?client=safari&rls=en&q=why+we+have+word+stress&ie=UTF-8&oe=UTF-8
https://www.google.com.hk/search?client=safari&rls=en&q=Why+English+have+sentence+stress&ie=UTF-8&oe=UTF-8
