◆on the contrary 恰恰相反、相反地
Use “on the contrary” when you have just said or implied that something is not true and are going to say that the opposite is true.
用来表示与先前的看法相反或极不相同，或表示先前看法的不是真的，现在说的才是真的。
When I first met him, I thought he was a modest and gentle person. On the contrary, he is arrogant and ruthless.
A: I hear you enjoy running. B: On the contrary, I find it to be tiresome.
by contrast, in contrast (to/with) 对照之下、与……成对比
Use “by contrast” or “in contrast (to/with)” to show that you are mentioning a very different situation from the one you have just mentioned.
In contrast 和 by contrast 意义相同，都是用来对比两件事或两个人之不同处。但他们的用法不尽相同。 In contrast 通常会与 to 或 with 连用，用法如下:in contrast to/with+名词。
In contrast to the diligent bee, the butterfly seems to fly around without a clear purpose.
In contrast with most local programs, the federal government’s plan looks beyond just economic growth.
Cats usually sleep in the day. Dogs, by contrast, never settle down.
◆on the other hand 另一方面
Use “on the one hand” to introduce the first of two contrasting points, facts, or ways of looking at something. It is always followed later by on the other hand or on the other.
是对同一件事物，提供不同角度或切入点，或对刚才的说明再加入一个不同的事实。
The writing class is taking up too much of my time; on the other hand, I’m learning a lot about writing.
I hate working in a clothing store, but on the other hand, there are also some advantages.
总结来说，在写文章的时候，如果你已经预设了立场，要表达与之前的说法相反或强调之前的说法是错误的，可以用 on the contrary。
若要做客观的观点对比，不加入个人对错想法，只是单纯比较时就用 by contrast 或 in contrast (to/with)。
而 on the other hand 则是说明一件事情的两面，或是不同的看法，虽有部分人士认为此片语不够正式，但在学术语料库出现的频率可是这三个里面最高的。
