by、through、via的用法及区别

1、by：在旁边，从旁边，到旁边（强调从旁边经过或路过）

关于by一词，记忆中课本上教给我们的主要有下面几个意思：
（1）附近，如nearby，pass by，go by，sit by the window等；
（2）被，如被动语态中的something is done by somebody；
（3）截止到……为止，如 Can you finish the job by 9 o'clock?
（4）乘坐，如by train/plane/water/sea/ship等。

其实呢，上面几个意思都知识by的简单化、实用化理解，不是它的意义核心。by的本义是指“（在/从/到）旁边”，也就是说：
（1）pass/go by是指从旁边经过或走过；
（2）something is done by somebody是指某事在某人身边（旁边）被做完，借指某事由某人完成；
（3）by 9 o'clock是指在9点钟附近（或左右），因为当有人问你要时间表的时候，基本上是希望你在某个时间点之前完成，如果在之后完成则说明那个时间点定得没有多大意义。
（4）by train等短语是指在火车近旁或者火车在自己近旁，借指自己在火车上。

在归纳出并抓住了by的本义之后，我们就会发现by其实并不是用来表示“经过、通过”的，它的这一意思是借用出来的，是用法所致。或者说，即便用by表示“经过、通过”的意思，也是“从旁边”经过或路过，所有的抽象用法都是由此衍生出来的。

2、thru / through：贯穿，穿过，透过，通过（强调从内部穿透）

through一词比较简单，thru是老美喜欢用的through的同音替代词（简化词），它们指的是从事物的内部穿透过去，比如说，光线透过眼镜的镜片进入我们的视网膜，河流穿过峡谷或城镇，某人闯过某片树林或丛林等等。注意：这个内部可以是完全封闭的（比如身体），也可以是部分封闭的（比如地表或峡谷），甚至可以是开放的（比如某一扇墙壁或门板）。through的核心意思是从中穿透或贯穿。

3、via：经由，途径，从某处（强调通过中间的媒介达成目的）

via一词似乎用得较少，日常生活中我们经常喜欢用by而不用via，比如要表达“发邮件”或“以邮件的方式”，基本上多数人第一个想到的就是by email，其实这时候用介词by的话，严格说起来是错误的用法，正确的做法是用via。

前面已经分析过by的本义，很明显by表示“通过某种方式或途径”的用法（如by train / by means of等）是借用或引申推广出来的，但by在表示该意思的时候有个前提：主体自己要跟随工具在一起，这是by的本义（在附近、在旁边）所决定的，或者说，主体和工具不能发生分离（这是by与via的本质区别）。

而via表达的意思是“经由某个人、某个区域、某个工具达到某个目的”，这里的“人/区域/工具”都是中间媒介，它们起着传递、连接等作用，这时候主体跟工具是注定要分离的。也就说：
（1）send someone a note via email 是指经由email的传递给某人发个便条通知某人某事情；
（2）travel from A to C via B 是指从A地出发经由B地前往C地；
（3）broadcast via satellite 是指经由（或通过）卫星进行进行广播。

【补充】也许有人会说，很多字典和词典上by也有via所表达的意思，那我只能这样跟你说：那是一些人不严格的用法，或者，是对方在不明白二者区别的情况下误用了而已（但不影响意思的理解），再或者，对方那样用是借用了by的抽象意义（不过这种解释似乎有点拧巴，包容一点的话也能接受）。

by、 through 的區別

1. through 是透過，通過某種途徑
He bought the vase through a dealer (n.).
他透過一個商人買到這花瓶。

2. by + v-ing：藉著做…，達成…目標。重點在陳述達成目標的方法。
He prepares for his finals by reviewing his notes.
他藉著/以復習他的筆記來準備他的期末考。

-He became rich through hard work (n.).
他透過努力工作而致富。

-He became rich by working hard (by v-ing).
他藉著/以努力工作而致富。

by, through, via 詳細解釋: http://tinyurl.com/kcezpd2

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English explanation:

The word “by" is most often used, and can mean the following:
1 near someone or something; at the side of someone or something
-The telephone is by the window.

2 used to show who or what does, creates, or causes something
-He was knocked down by a bus.

3 used for showing how or in what way something is done
-The house is heated by gas.
-to travel by boat/bus/car/plane
to travel by air/land/sea

4. used to show the degree or amount of something
The bullet missed him by two inches. House prices went up by 10%.

more uses: http://oaadonline.oxfordlearnersdictionaries.com/dictionary/by

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“Through" generally means to go from one end of something/place to the other.

1. from one end or side of something or someone to the other
-The bullet went straight through him.Her knees had gone through 
-The sand ran through (= between) my fingers.

2. see, hear, etc. through something to see, hear, etc. something from the other side of an object or a substance
-I couldn’t hear their conversation through the wall.

3. past a barrier, stage, or test
-Go through this gate, and you’ll see the house on your left.

4. (also informal thru) until, and including
We’ll be in New York Tuesday through Friday.

5. by means of; because of
-You can achieve success through hard work/by working hard.

more: http://oaadonline.oxfordlearnersdictionaries.com/dictionary/through
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“Via" emphasizes by someone or something.

1. through a place
-We flew home via Dubai. 
(This use is synonymous with “through/thru."

2. by means of a particular person, system, etc.
I heard about the sale via Jane.The news program came to us via satellite.

(This use is synonymous with “by.")

source: http://oaadonline.oxfordlearnersdictionaries.com/dictionary/via

So at times, the words are interchangeable, but they all emphasize different things.

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