Primary vs Secondary Sources: Key Differences

The distinction between primary and secondary sources depends on what you are researching and how the source relates to your topic. A primary source is original material: something created at the time of the event, or by a direct participant. A secondary source analyzes, interprets, or describes primary sources.

The same document can be a primary source for one research question and a secondary source for another. A newspaper article from 1945 is a primary source for studying World War II public opinion but a secondary source for studying the history of a specific military campaign (where government documents and battle reports would be primary).

The Core Distinction

Primary vs Secondary Sources by Discipline

The type of source considered "primary" varies by field:

What Counts as a Primary Source: Examples

Historical research:

• A letter Abraham Lincoln wrote to General Grant in 1864
• A photograph taken in a factory in 1910
• A speech transcript from the civil rights movement
• U.S. Census data from 1930

Scientific research:

• A journal article reporting original experimental results (e.g., a randomized controlled trial)
• A dataset of climate temperature readings
• A case report describing a rare medical condition
• A genome sequence deposited in a public database

Literary analysis:

• The text of Hamlet
• A letter Shakespeare wrote (hypothetically)
• A contemporary performance review from 1603

Social science research:

• Interview transcripts you collected
• Survey data you gathered or downloaded (e.g., from the General Social Survey)
• Government administrative records (census, vital statistics)
• Video recordings of behavior

What Counts as a Secondary Source: Examples

Historical research:

• A biography of Abraham Lincoln
• A textbook chapter on the Civil War
• A documentary about the 1960s civil rights movement

Scientific research:

• A systematic review of randomized controlled trials on a treatment
• A meta-analysis combining results from 30 studies
• A textbook chapter on molecular biology

Literary analysis:

• An academic article analyzing the use of soliloquy in Hamlet
• A book-length study of Shakespeare's tragedies

Social science research:

• A literature review synthesizing studies on poverty and education
• A book summarizing theories of organizational behavior

Tertiary Sources

Some frameworks distinguish a third category: tertiary sources compile and index primary and secondary sources without analyzing them directly.

Encyclopedias (including Wikipedia) are typically tertiary sources. They are useful for getting oriented on a topic but are generally not appropriate to cite in academic papers as primary or secondary evidence.

When to Use Primary vs Secondary Sources

Use primary sources when:

• You are presenting original evidence or data to support your argument
• Your research question is about what happened or what was said, not what scholars think about it
• You are doing historical, literary, or archival research where the original material is the subject
• You need to ground your claims in direct evidence rather than another author's interpretation

Use secondary sources when:

• You want to understand how scholars have analyzed or interpreted primary material
• You need theoretical frameworks or established definitions
• You are situating your work within existing literature
• You want to show what the current state of knowledge is on a topic

Most academic papers use both. Primary sources provide the evidence; secondary sources situate the evidence in the field's ongoing conversation.

How to Identify Source Type

Ask: Was this created by a direct participant in or observer of the event being studied, or by someone analyzing it afterward?

If created by a participant or observer at the time: primary. If created afterward by someone analyzing the original event or material: secondary.

Ask: Is this reporting original data or findings, or synthesizing and interpreting someone else's findings?

Original data or findings: primary (in the sciences and social sciences). Synthesizing and interpreting: secondary.

Remember: The classification depends on your research question. A 2020 textbook is primary source evidence for a study of contemporary science education; it is a secondary source for a study of quantum mechanics.

Frequently Asked Questions

What is the difference between a primary and secondary source? A primary source is original material created at the time of the event or by someone directly involved: a diary entry, a speech, original research data, or the text of a novel. A secondary source analyzes or interprets primary sources: a biography, a literature review, a textbook, or a scholarly article analyzing someone else's research. The same document can be primary for one research question and secondary for another.

Is a textbook a primary or secondary source? A textbook is almost always a secondary source. It summarizes and synthesizes existing research rather than presenting original data or firsthand accounts. The exception would be if you are studying the textbook itself as an artifact, for example, in research on how science is taught to undergraduates, a textbook would be a primary source.

Is a journal article a primary or secondary source? It depends on the type of journal article. An original research article reporting new experiments, data collection, or findings is a primary source. A review article or meta-analysis that synthesizes other studies is a secondary source. In the humanities, a scholarly article analyzing a poem or historical event is a secondary source; the poem or original documents are primary.

Is Wikipedia a primary or secondary source? Wikipedia is a tertiary source. It compiles and summarizes information from primary and secondary sources but does not constitute original research or analysis. It is generally not appropriate to cite in academic papers, though it can be useful for initial orientation on a topic. The sources cited in Wikipedia articles may be primary or secondary, and those are the sources you should access and cite directly.

How many primary sources should a research paper have? This depends on the type of paper and field. In empirical sciences, a research paper typically cites many secondary sources (prior studies) and presents its own primary data. In history or literary studies, heavy reliance on primary sources is expected; a historical thesis might be built almost entirely on archival primary sources with secondary sources providing interpretive context. In most undergraduate papers, a mix is appropriate: secondary sources for context and theoretical framing, primary sources for direct evidence.

For guidance on evaluating and using sources effectively, see how to write a literature review and how to paraphrase.