Types of Evidence

Quotations and Paraphrase<

Quotations are exact reproductions of someone else's words. When you quote someone, you must make sure that you reproduce the exact words of your source. You must also make it clear to your reader that the words you reproduce are someone else’s by placing them within quotation marks (“ ”) or in an indented block quote. If the quotation you want to use is too long, you can cut out a piece of it and replace it with an ellipsis (. . .), as long as you are not changing or distorting the original meaning. For example, in an essay on freedom of speech, a student quotes the first amendment:
The first amendment clearly prohibits federal legislators from restricting citizens’ right to express themselves: “Congress shall make no law . . . abridging the freedom of speech, or of the press.”

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A paraphrase, on the other hand, is more like a summary of what someone else has said. If you choose to paraphrase someone else’s work, you do not need to place it within quotation marks. However, you must be careful not to plagiarize accidentally the work by using its exact words without using quotation marks. In that same essay on freedom of speech, the student paraphrases the first amendment:
The first amendment, of course, protects every citizen’s right to express his or her opinions through the press, public demonstration, or petition, while restricting the government’s ability to interfere with any citizen’s religious beliefs.

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You should always use quotations when the exact words that you are reproducing are important, as is the case in a discussion of a law or a poem. A paraphrase, on the other hand, can be used when you only need to give your reader the basic idea of another’s words—the conclusions of a recent scientific study, for example, or a summary of an expert’s opinion. Both quotations and paraphrases require citations.

Photographs and Diagrams<

Visual images are frequently used as evidence. This is especially true when a long, wordy summary will be confusing to readers without an accompanying illustration. Reproducing a photograph, a drawing, a painting, or a diagram can save you a lot of space in an essay. However, simply including an image may not be enough. Most visual images demand some explanation in words—specific features to look for, a few ideas to think about, or some kind of context. Photographs or reproductions of visual images can be used as evidence for a variety of purposes. An art history essay on Dutch painting, for example, might include an image of a particularly famous portrait by Rembrandt. An anthropology paper might also use photographs of a culture’s artifacts that would be difficult to describe in words, such as clothing or tools. Alternately, a writer might use a photograph for more practical purposes. A community group arguing that its city’s local highways are in need of repair might include a picture of a major road filled with potholes.

Diagrams are visual images used to explain ideas or structures that would be difficult to describe in words alone. Many writers find that diagrams are useful to illustrate complex information. In an essay on English history, for example, you might include a family tree of English royalty, or a timeline of historical events. In a paper explaining the mechanics of a jet engine, your readers may require a diagram of the engine, its parts, and their names. In a write-up of a scientific experiment on the effects of an antibiotic, it may be useful to offer your reader a diagram of its chemical structure.

All photographs or reproductions of visual images require a citation (even if you are the photographer); you must let your reader know who is responsible for the photograph. If you reuse a diagram created by another author or illustrator, you must cite the source. If you create your own diagram, you do not need to cite yourself as a source; if you get the information that you use for your diagram from a specific source, however, you’ll have to provide a citation.

Historical Facts<

Historical facts are frequently used as evidence, especially in papers that consider what has happened in the past. These facts are often events that have a date or time period attached to them: the year of a major political election, the years when a war was fought, the founding date of a country or major institution, the publication of a major book, or the death of an important figure. More often than not, you will use dates to provide some context for your argument—to show that an important event happened at a certain time. Citing historical facts can sometimes be tricky. Depending on your readers, many of these famous events can be so well known that they do not require a citation. The fact that the American Declaration of Independence was signed on July 4th, 1776, for example, is well known, even outside America. If you or your reader didn’t happen to know this offhand, either of you could find this information in any encyclopedia or dictionary; any source would provide the same information. Some historical facts are much more obscure, however, and may require a citation. The guideline here is this: you must cite your sources if you can only find the historical fact in one work or a few works, such as a book on a specific historical period or a document from that period. If this is the case, it is likely that it took one historian a good deal of work to uncover facts that few people knew about. For example, if you want to point out that the Supreme Court made a certain ruling on a specific date—and this ruling is not a commonly known fact—you may have to cite the court records to prove to your reader that this ruling actually occurred.

Direct Observations<

Some arguments are supported with evidence that writers gather on their own. A movie reviewer, for example, might point out that several audience members walked out during the movie that she is reviewing. A journalist might report events that he or she saw during a riot or public demonstration that were not caught on film. Sometimes, too, visual evidence cannot be adequately described with just a photograph; a geographer, for example, may need to supplement a photograph of a site with his own further description of what it looks like. Such evidence, however, depends solely on how much your readers trust your observations. If you want to use this type of evidence, you’ll need to make sure your readers will accept your word on trust alone. More often than not, though, professional writers have to offer other forms of evidence—such as photographs, quotations, or numerical data—to help support their observations.

Numerical Data<

Data are sets of facts gathered together in one place for your reader. Data can be any kind of information, but we usually think of data as numbers. Readers in the sciences and social sciences like economics expect numerical data more than any other kind of evidence, as do many professional readers (government officials or corporate managers, for example). On the other hand, other readers (like an English teacher) may not be interested in numerical data, since they expect to read arguments about issues where numerical data is unavailable or not important. Numerical data can be described in words:
According to the Department of Labor, the unemployment rate rose to from 4.9% in January of 2008 to 7.6% in January of 2009, an increase of 2.7 percentage points and 4.1 million unemployed people.

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Or in visual charts:

U.S. Unemployment Rate, January 2008-January 2009<

DatePercent
Jan 20084.9
Feb4.8
Mar5.1
Apr5.0
May5.5
Jun5.6
Jul5.8
Aug6.2
Sep6.2
Oct6.6
Nov6.8
Dec7.2
Jan 20097.6
Unemployment Chart

Source: Bureau of Labor Statistics, February 10, 2009.