Whether you do academic or work-related research such as strategic planning, it’s important to look for the right type of source that will yield the information you need. You can consider sources by the type of information they provide, or by the type of publication in which the source resides. Know that there’s overlap—these are not discrete categories. It’s useful to consider types of sources in different ways to help you consciously choose sources that will yield the best evidence for your thesis, purpose, and audience.

Type of Source by Information

There are three basic types of information, primary, secondary, and tertiary, although tertiary sources are sometimes grouped with secondary. Primary sources are original works, secondary sources are analyses of those original works, and tertiary sources are collections of secondary source information. Academic, scientific, and business professionals use all three types of sources, as appropriate. You’ll determine appropriateness by understanding the type of support your thesis, purpose, and audience require, as well as understanding the different types of support themselves.

• Primary sources are original works (e.g., original historical documents, art works, interviews, diaries, photographs, speeches). They allow researchers to get as close as possible to original ideas, creative works, and contemporary accounts of events, as well as empirical research (observations, direct experience, and experiment results).
• Secondary sources contain others’ insights into and analyses of those primary works (e.g., scholarly articles about historical documents, art works, or interviews; biographies; commentaries). Secondary sources analyze, review,  interpret, and/or evaluate information in primary resources or other secondary resources.
• Tertiary sources provide overviews of topics by synthesizing information gathered from other resources (e.g., encyclopedias, dictionaries). Tertiary resources often provide data in a convenient form or provide the context with which to interpret information.

Type of Source by Publication

Another way to categorize sources is by the type of publication in which they reside. Considering sources by type can answer that lingering question about why useful and informative Wikipedia articles are often considered inappropriate sources for academic research. Again, all types of sources have their legitimate uses, although using specialized or scholarly sources is the goal for academic work.

Overview Sources

Encyclopedias, Wikipedia articles, and general Google searches are good places to begin your research to get an overview of your topic and the big questions associated with that topic. But you should not use these as your main sources for an academic essay simply because they are too general. Instead, use these sources to develop context for your topic—to learn the background of the topic, major ideas and subtopics, and important researchers in the field, for example. You can usually find overview sources through general Google searches. Be careful, though, when doing general Google searches. You may find websites that are not credible because they are not written by people knowledgeable in the field, or because they are slanted and present only one side of an issue.

Reports, articles, and books from credible non-academic sources

General interest magazines (Time, Newsweek online) or online general news sites (CNN, MSNBC) can be used as overview materials, but also may provide more in-depth coverage of a topic for the general pubic. For example, an article on the melting of the polar icecaps in Time magazine may offer overview of the issue, while an article on polar icecaps in Scientific American or The Ecologist, while still written for a general reading audience, may go into more depth. “Credible” is the important characteristic here. Sources written for a general reading audience can be used if they offer well-researched and objectively-presented information about an issue, person, or event. Credible non-academic sources may offer more up-to-date information or initial research on events or trends not yet analyzed in academic literature, as well as point you to more specialized sources. You usually can find credible, non-academic sources if you do Google Scholar searches or look at other valid sources such as government websites (e.g., for polar icecaps, you might look at the website for the National Resources Defense Council/NRDC or reports found at the website for the National Snow and Ice Data Center/NSIDC). You can also look in article databases to find credible, non-academic sources.

Scholarly Sources

Scholarly or specialized sources are written for readers with some background in the particular topic. For example, someone with a background in science should be able to easily read and understand the articles published in the Proceedings of the National Academy of Sciences or the Journal of the Atmospheric Sciences. However, even if you are not a specialist in the field, your initial reading of overview material and information from credible sources written for the general public should enable you to use some specialized material.  Scholarly articles are the result of rigorous research and analysis. They usually provide strong, researched, logical evidence for claims. Scholars write articles about what they’ve done in their research, what they’ve found, and why they think it’s important, to join the academic conversation around a specific topic. To be published, scholarly articles and books have to be peer-reviewed, which means that other known scholars in the field have to evaluate and recommend those articles for publication. You usually can find scholarly articles from databases that draw from academic publications.

To determine if a source is scholarly, look for the following characteristics:

• Structure: The full text article often begins with an abstract or summary containing the main points of the article. It may also be broken down into sections such as “Methods,” “Results,” and “Discussion.”
• Authors: Authors’ names are listed with credentials/degrees and places of employment, which are often universities or research institutions. The authors are experts in the field.
• Audience: The article uses advanced vocabulary or specialized language intended for other scholars in the field, not necessarily for the average reader.
• Length: Scholarly articles are often, but not always, longer than the popular articles found in general interest magazines such as Time, Newsweek, National Geographic, etc. Articles are longer because it takes more content to explore topics in depth.
• Bibliography or Reference List: Scholarly articles include parenthetical in-text citations referring to items in a bibliography or reference list. A list of sources at the end is important so others can find the original source of an idea or quotation.

The video below summarizes sources by both type of information and publication.

How to Determine What Type of Source to Research

Analyze your topic/working thesis to determine the types of sources that can help support that thesis. For example, if your topic deals with Van Gogh’s use of pale green paint and what it connotes in his later paintings, you will need to blend evidence from primary sources (images of the paintings themselves) with secondary sources (other scholars’ views, discussions, and logical arguments about the same topic). If your working thesis deals with the benefits of regular exercise for older adults in their 70s-90s, you may blend evidence from primary sources (uninterpreted data from research studies, interviews with older adults or experts in the field) with secondary sources (interpretations of research studies). In some cases, you may find that your research is mostly from secondary sources and that’s fine, depending on your topic and working thesis. Just make sure to consider, consciously, the types of sources that can best be used to support your own ideas.  And, make sure that the sources you use are mostly scholarly sources.