By the time you finish this you unit, you should:
  • know the difference between facts and interpretation;
  • know how to evaluate a source's credibility;
  • be able to distinguish between primary and secondary sources;
  • know the meanings of the terms below.


  • ad hominem 
  • agenda
  • bias
  • credibility
  • fact
  • interpretation
  • logical fallacy
  • objectivity
  • post hoc 
  • primary source
  • red herring
  • secondary source
  • subjectivity
  • tone


The following Internet and print sources can help you with the concepts covered in this unit:
  • The Ready Reference Handbook contains sections on logical fallacies and credibility (49b).

Updated January 5, 2001
© Mark Canada, 2001

Evaluating Sources

Your argument is only as good as your information.  If the support you provide is inaccurate or biased, then no amount of clarity, organization, depth, or style will make your argument compelling, at least to readers who recognize the holes in your information.  Thus, once you have located relevant sources, you next need to evaluate them.  In particular, you need to determine whether they contain factual material, interpretation, or a combination of the two.  You also must assess each source's credibility.  Finally, you should determine whether they are primary or secondary sources and try to draw from both types.

Facts and Interpretation

Probably every source you encounter will include factual material, which is material that most people accept as indisputable.  Some examples of facts are dates, quantitites, names, and locations.  One test of whether something is a fact is to ask yourself whether it answers one of the following questions: Who? What? When? Where?  If it does, it likely is a fact.  For example, the material in the following sentence is entirely factual: Benjamin Franklin began publishing the Pennsylvania Gazette in 1828 in Philadelphia.  Factual material can strengthen an argument because it cannot be disputed and thus provides a solid foundation.  An interpretation, on the other hand, involves a conclusion that someone, such as a scholar, has drawn from the facts and thus is disputable.  Some examples of interpretations are value judgments, explanations of causes and effects, assessments of meaning, and proposals.  You can test whether something is an interpretation by asking yourself whether it answers one of the following questions: Why? How?  If it does, it probably is an interpretation.  For example, the following sentence contains some interpretation: Benjamin Franklin believed humans could control their destiny and wrote his autobiography to encourage them to exercise their free will.  Interpretation strengthens an argument by giving it meaning and substance.  Indeed, as you will see later, an argument by definition must include some interpretation.  As you also will see, you must give credit to sources when you borrow their interpretations.


When you assess a source's credibility, you try to determine how believable it is.  First, you should look at the credentials of the author and the publisher.  Authors who have advanced degrees in their fields, who work for reputable organizations such as respected universities or government agencies, or who have published other books or articles tend to be more credible than authors who lack any of these credentials.  Furthermore, well-known publishers--especially those affiliated with reputable universities--tend to be more credible than other publishers because they have reputations to uphold.  In other words, credentials provide some proof that the material in a source is accurate and based on sound reasoning.  Because it is much easier to publish material on the Internet than to print it in a book or reputable magazine, print sources tend to be more credible than sources you find on the Internet.  A second consideration is timeliness.  Sources published or posted recently tend to be more credible than older sources simply because new knowledge gradually becomes available as scholars continue to conduct research.  You also will want to look for sources whose authors appear to have considered various interpretations and to have presented fair accounts.  Beware of biased sources, which tend to present only evidence that supports one interpretation.  In particular, try to avoid a source that has an agenda: a set of political, ideological, or financial goals that the author or authors seek to achieve.  One clue that an author has an agenda is a subjective tone--that is, one with an emotional component; stick with objective sources, which avoid emotional language.  Finally, evaluate the reasoning in a source's argument.  Try to avoid sources that rely on logical fallacies, false arguments that tend to distract or mislead readers or listeners rather than stand on reasoning and support.  Here are three common logical fallacies:
  • The phrase "ad hominem," a Latin phrase meaning "to the person," refers to an argument that is really only a personal attack.  The following sentence contains an ad hominem fallacy: "As someone who never served in the military, my opponent lacks the qualities to be a great leader."
  • A red herring is a point that tends to distract the reader or listener rather than to build an argument.  For example, in an argument against gun control, the following statement would be a red herring: "Some of America's greatest heroes owned guns."
  • The phrase "post hoc," Latin for "after the fact," refers to an argument that suggests that one event caused another simply because it took place first.  In reality, other factors may have led to the second event.  The following sentence contains a post hoc fallacy: "The television program Walker, Texas Ranger has positively affected safety in the United States; since it went on the air, violent crimes have decreased."

Primary Sources

What they are: Think of primary sources as collections of raw data requiring interpretation.  In many cases, they contain mainly factual material--that is physical descriptions, dates, locations, quantities, and other types of information that people generally agree is true.  It is a good idea to start your research by looking at primary sources so that you can develop your own ideas.  Here are a few kinds of primary sources:
  • Works of art--including novels, short stories, poems, plays, paintings, sculptures, films, symphonies, and songs--express authors' feelings and ideas.
  • Personal narratives, such as letters and diaries, contain factual information about people's lives.
  • Many forms of journalism, including newspaper stories and television broadcasts, report facts about events in politics, business, sports, and other fields.
  • Some government documents, such as statistics from the U.S. Census Bureau, contain statistics on population, financial matters, education, and other subjects.
How to find them: Run searches on a library catalog such as Brave Cat or specialized databases such as News Bank.  For statistical data, a good place to start is the Statistical Abstract of the United States.  In some fields, such as psychology and linguistics, you can create your own primary sources by conducting surveys, interviews, or observations.  While most primary sources are still available only in print form, a vast amount of primary material is available on the Internet and can be found on World Wide Web sites such as those managed by the University of Virginia and the U.S. Census Bureau.

Secondary Sources

What they are: Secondary sources contain interpretations of raw data  The authors of secondary sources, often university professors and other scholars, analyze factual material and draw conclusions about causes, effects, and meanings.  Others may disagree with their conclusions and offer their own interpretations in separate secondary sources.  After you have begun to interpret primary sources, you can use the material in these secondary sources to qualify, support, and refine your interpretation.  Be careful, though.  Scholarly books and articles often contain very challenging language. Keep a dictionary and a subject encyclopedia at hand when you read them.  Here are a few kinds of secondary sources:
  • Subject encyclopedias are invaluable secondary sources, especially early in the research process, because they provide useful background information, are highly credible, and often contain brief bibliographies--lists of other useful sources on a particular subject.
  • Scholarly books, generally written by university professors who are experts in their fields, often provide very useful and thorough overviews of a particular subjects.  Start by reading the introduction and then skim the individual chapters for relevant information.  Finally, check the book's bibliography for other sources.
  • Scholarly journal articles, also written by experts, usually cover very specific topics.  Like popular magazines, scholarly journals appear periodically, but they contain information designed for experts, rather than the general public. 
How to find them:  One of the best places to start when looking for secondary sources is the library's reference section, where you can find thousands of subject encyclopedias.  To find scholarly books, run searches on a library catalog such as Brave Cat or research databases, which are computer resources listing thousands of books and articles in particular fields. Type in the name of a topic, title, author, or a key word. Several databases are available on the Sampson-Livermore Library Web site. If you wish to search a database when you are off campus, you may need a password. Call the library's reference desk (521-6265) for information about getting a password. You also can find scholarly books and articles by checking bibliographies.  Whenever you come across a book or article on your topic, check the end for a bibliography and copy down the citations for other books and articles on your topic. Use these citations to find the materials. In many cases, you will have to use interlibrary loan, a service through which you can order books and photocopies of articles from other libraries, often at no cost to you. If an item you need is not available at our library, ask a librarian about interlibrary loan. Once you understand the process, you can order materials by visiting the library's Web site and typing in the appropriate information. Because it usually takes about a week or two to receive an item through interlibrary loan, you should order these materials as soon as possible. 


  1. Distinguish Between Facts and Interpretation: Identify a fact and an interpretation in one of your sources.  Explain the difference.
  2. Assess Credibility: Use the tips above to assess the credibility of one of your Internet sources.  Consider the author's and publisher's credentials, timeliness, bias, tone, and logical fallacies.
  3. Distinguish Between Primary and Secondary Sources: Choose one of your sources and explain why it is a primary or a secondary source.  Identify the source further by labeling it as a diary, letter, subject encyclopedia, scholarly journal article, or something else.
  4. Draft Annotation: Using what you have learned in this unit, write an annotation of one of the sources you are using for your group's definition article and post it on the group's World Wide Web page.  See my description of the assignment on the syllabus for details about content and format.