Comparison和Contrast都有“比较”的意思，但是二者由于目的不同，表现形式和带来的作用都有比较大的差异。
为了区分我将Comparison翻译成“类比”，Comparison类比的目的是为了“比同”，找到事物之间的共同点，通过熟悉的事物来了解不熟悉的事物（to present information about something unfamiliar by comparing it with something familiar）。
而Contrast对比的目的是为了“比异”，寻找事物之间的差异，从而凸显其中一个事物的某一方面的特质(to highlight the superiority of one thing by contrasting it with another ),吸引读者注意力(draw reader’s attention)。
我们来集中看一下Comparison和 Contrast的标志词：
Comparison类比
like
resemble
similarly
likewise
same
as well as
alike
in the same way
in a similar way
equally
Contrast 对比
instead
yet
nevertheless
but
conversely by contrast
on the other hand
as opposed to
on the contrary
differently
while
to the contrary
我们分别看一下具体的例子：
2.2.2.1 Comparison类比
If the medical sector worked like the charity sector did, we'd still be using leeches instead of antibiotics. That's because a few hundred years ago, we collectively decided that the best way to determine what happens in reality wasn't to argue about it from the armchair, but to go out and do experiments and observe the results. As a result, we've gone from useless bloodletting to successful brain surgery. However, half a millennium later, the field of charity still hasn't learned this lesson.
（节选自Joey Savoie, “Charity Needs a Scientific Revolution and We Can Make it Happen”）
Joey Savoie这篇文章呼吁慈善机构通过科学手段的改革提高效率。 选段将charity和medical sector类比，指出医学正式因为经历无数试验和观察才能从早期迷信无用的放血疗法发展到目前高精的医学手术。与之相似，charity如果想要发展也不能坐在屋里纸上谈兵，而是要通过科学的途径慢慢提升自身的水平，而遗憾的是charity至今也没有想明白这个问题。通过这个类比，作者能够更加生动地(vividly)表现出自身对于charity发展缓慢的现状的担忧，希望慈善组织可以通过科学的途径取得应有的进步。
If you were in an emergency room and the hospital could either save you and five other people or save a single individual, I don’t think you’d say either outcome is equally good and it doesn’t matter what the hospital does. This situation is actually quite similar to the one we face when deciding where to give our money. The fact is that when acting as individual donors, sadly, each of us can’t single-handedly solve all of the world’s problems. So when donating it makes sense to try to do the best we can by giving to effective charities that can do the most good possible with our money.
（节选自Joey Savoie, “Charity Needs a Scientific Revolution and We Can Make it Happen”）
在将charity与medical sector类比后，作者又将charity比作emergency room。急救室有效率高低之分，慈善机构同样如此。通过人们比较熟悉的急救室的类比，读者可以更好地理解在捐助者个人能力有限的情况下为何应当选择那些效率更高的，能够将我们的钱充分发挥作用的慈善机构。
2.2.2.2 Contrast 对比
A strange thing has happened in the American arts during the past quarter century. While income rose to unforeseen levels, college attendance ballooned, and access to information increased enormously, the interest young Americans showed in the arts—and especially literature—actually diminished.
（节选自Dana Gioia, “Why Literature Matters”）
这篇文章中作者主要想唤醒读者对于阅读文学重要性的意识(arouse reader’s awareness)。第一自然段首先描绘了社会宏观经济，教育和信息领域的高速发展，这样一片繁荣的景象与后半句话中强调的文学阅读的下降形成了极大的反差。当读者醉心于欣赏前半句描绘的美好社会景象时，按照常规的逻辑，人们在如此舒适便利的条件下一定会阅读更多书籍，然而“strange”（奇怪）的是文学的阅读量“actually”（事实上）下降了。如此戏剧化的反转（dramatic contrast）给读者非常强的冲击力(great impact)。
Reading is not a timeless, universal capability. Advanced literacy is a specific intellectual skill and social habit that depends on a great many educational, cultural, and economic factors. As more Americans lose this capability, our nation becomes less informed, active, and independent minded. These are not the qualities that a free, innovative, or productive society can afford to lose.
（节选自Dana Gioia, “Why Literature Matters”）
在文章的结尾段，作者警告(warn)如果美国民众继续不重视阅读，慢慢失去这项技能后，美国就会向着“less informed, active, and independent minded”的方向发展，这与民众心目中“free, innovative, or productive”的社会预期形成极大的反差。这种反差刺激了美国大众的民族荣誉感(nationalism)和自尊心(pride)，将文章升华到一个更高的层面，从感性层面进一步让读者意识到阅读下降带来的严重影响，呼吁读者重视阅读。
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