What Is a Tertiary Source? | Definition & Examples

Tertiary sources compile the information contained in primary and secondary sources without adding novel interpretations or ideas. Examples of tertiary sources, also known as reference works, include:

• Encyclopedias
• Dictionaries
• Bibliographies
• Databases

Tertiary sources gather information from many different types of sources. They can include lists, summaries, and indexes of primary sources, which present novel ideas or provide direct evidence and secondary sources, which offer interpretations or analyses of primary sources.

Tertiary sources are a valuable resource during the research process as they can provide background information and indicate where to look for primary and secondary sources. They can highlight key terms you should know as well as researchers whose work is especially pertinent to your topic.

That said, tertiary sources are generally not suitable for direct reference in academic writing.

What is a tertiary source?

Research sources can be divided into three types:

• Primary sources: These involve original research with novel findings or provide firsthand evidence (e.g., documentary footage, speech transcripts, personal letters)
• Secondary sources: These offer analyses or interpretations of primary source evidence or findings (e.g., journal articles, reviews)
• Tertiary sources: These are reference works that use primary and secondary sources to provide an overview of the topic (e.g., databases, indexes, encyclopedias)

Academic writing generally relies on primary and secondary sources that you can interpret and use to develop your arguments.

Tertiary sources do not engage with the information they present in an analytical way. Rather, they compile information from primary and secondary sources to give a thorough background on the topic. For this reason, they are useful in the initial stages of the research process as a jumping-off point, but they are not typically suitable for citation within your paper.

Examples of tertiary sources

The information given by tertiary sources includes key terms and definitions as well as overviews of the topic and lists of useful sources.

• Bibliographies, indexes, timelines, databases, and directories put information in order and provide references to relevant primary and secondary sources.
• Encyclopedias, dictionaries, textbooks, and manuals list key words and definitions as well as include topic overviews drawn from primary and secondary sources.

Primary vs secondary vs tertiary sources

Unlike primary and secondary sources, tertiary sources do not engage in analyses or interpretations of the information they provide.

However, depending on your research problem and the way you engage with a source, a typical tertiary source could function as a primary or secondary source.

For example, dictionaries are generally tertiary sources, but if you are researching the evolution of a particular word over time, you might cite dictionary entries from different periods as direct evidence of your argument.

The following questions can help you evaluate whether a source is tertiary:

• Is the source itself the object of analysis, or does it only provide background information?
• Does the source give a firsthand account or original data (primary) or interpret other sources (secondary)? Or does it list or summarize information from other sources (tertiary)?

Using tertiary sources

While tertiary sources are usually credible and therefore fine to consult, they are often anonymous and general rather than specialized in the given topic. A higher degree of specificity is generally expected from the sources you cite in academic writing, but tertiary sources can still be of benefit to you during your research process.

When you’re starting your research, you can use tertiary sources to:

• Collect background information
• Learn current views on the topic
• Identify key figures whose work may be useful to you
• Pick out keywords and terms

You can then build on this information through more in-depth research into primary and secondary resources.

Frequently asked questions about tertiary sources

How are tertiary sources different from primary and secondary sources?

Primary sources involve original research with novel findings or provide firsthand evidence (e.g., photographs, records, official documents).

Secondary sources offer analyses or interpretations of primary source evidence or findings (e.g., journal articles, reviews).

Tertiary sources are reference works that use primary and secondary sources to provide an overview of the topic (e.g., databases, dictionaries).

How do I tell if a source is tertiary?

Your research problem and the way you use a source will determine whether it is tertiary.

The following questions can help you evaluate whether something is a tertiary source:

• Is the source itself the object of analysis (primary or secondary), or does it only provide background information (tertiary)?
• Does the source give a firsthand account or original data (primary) or interpret other sources (secondary)? Or does it list or summarize information from other sources (tertiary)?

Can I use tertiary sources in my research?

Tertiary sources are generally not cited directly in academic writing. However, they can be useful as a jumping-off point when you begin the research process.

When you’re starting your research, you can use tertiary sources to:

• Collect background information
• Pick out keywords and terms
• Learn current views on the topic
• Identify key figures whose work may be useful to you

Tertiary sources can direct you to primary and secondary sources that you can use later during the writing process.