Quotations from experts’ opinion
Results of Study/Survey/Experiment等等。
根据论据在文章中所起的作用可以将论据分为四类，以The Official SAT Guide中的 " Let There Be Dark " 这篇文章中的论据为例：
第一类论据是难以辩驳的事实、数据或研究Fact, Statistics, Results of Study/Survey/Experiment：“Our bodies need darkness to produce the melatonin, which keeps certain cancers from developing, and our bodies need darkness for sleep.”
The author is sure to include hard evidence, an irreplaceable component of argument, in his article to support his claim. He refers to the function of darkness for our cancer prevention and sleep. This makes his work credible and believable and readers are confident of what we are being told is correct and true. The objective non-refutable fact backs up the claim that darkness is valuable. Without the evidence, his passage would not mean a thing to us readers and we would never be able to believe what he has said.
第二类论据是引用专家或专业机构的观点Quotations from experts’ opinion：“…the American Medical Association has voiced its unanimous support for ‘light pollution reduction efforts and glare reduction efforts at both the national and state levels.”
The author is able to build his point with the agreement of a respected authority, which we assume has great authority and are trustworthy. He quotes the American Medical Association’s support for reducing light pollution in the paragraph. The citation from the authoritative source gives writer credibility so the reader is more likely to agree with him. Through citing authorities’ opinion, the author successfully transfers their trust and belief in those authorities to his own argument.
第三类论据是时下的新闻或例子Current events and Examples：“Every religious tradition has considered darkness invaluable for a soulful life and the chance to witness the universe has inspired artists, philosophers and everyday stargazers since time began. In a world awash with electric light…how would Van Gogh have given the world his ‘Starry Night’?”
The author’s argument is furthered by his use of specific examples. By alluding to the function of night in religion, art, philosophy, and more specifically in“Starry Night”, a painting famous for its dark night, the author informs reader that there are something invaluable about darkness. This urges the readers to think that they should preserve this night; otherwise we would not miss a lot of human treasures. The cited examples help readers to see a particular demonstration of nights’ importance—how it plays out in the real world, and thus readers are more likely to agree with the author’s claim.
第四类论据是个人经历或名人轶事Anecdote and Personal Experience：“At my family's cabin on a Minnesota lake, I knew woods so dark that my hands disappeared before my eyes. I knew night skies in which meteors left smoky trails across sugary spreads of stars.”
The author starts his article off by recounting a personal story – a night spent on a Minnesota lake with skies “in which meteors left smoky trails across sugary spreads of stars”, which resonates with readers. Bringing in personal experience adds a human element to his argument that the night is too wonderful to lose. By drawing in his readers with a personal anecdote, the author generates a strong emotional connection and the readers will be filled with the same awe and love for the serene night with the author. This provides a baseline of sorts for readers to find credence with the author’s claims.