Imagine that an army conquered a small country 200 years ago, and as a Wikipedia editor you have the following sources:
- a proclamation of victory written at the time of the conquest,
- a diary written by someone who lived at the time and talks about it,
- a book written 150 years later, that analyzes the proclamation,
- an academic journal article written two years ago that examines the diary, and
- an encyclopedia entry written last year, based on both the book and the journal.
Both the proclamation and the diary are primary sources
. These primary sources have advantages: they were written at the time, and so are free of the opinions and fictions imposed by later generations. They also have disadvantages: the proclamation might contain propaganda
designed to pacify the conquered country, or omit politically inconvenient facts, or overstate the importance of other facts, or be designed to stroke the new ruler's ego. The diary will reflect the prejudices of its author, and its author might be unaware of relevant facts.
The book and the journal article are secondary sources
. These secondary sources have advantages: The authors were not involved in the event, so they have the emotional distance that allows them to analyze the events dispassionately. They also have disadvantages: In some topic areas the authors are writing about what other people said happened and cannot use their own experience to correct any errors or omissions. The authors may be unable to see clearly through their own cultural lens, and the result may be that they unconsciously emphasize things important to their cultures and times, while overlooking things important to the actual actors.
The encyclopedia article is a tertiary source
. It has advantages: it summarizes information. It also has disadvantages: in relying on the secondary source, the encyclopedia article will repeat, and may accidentally amplify, any distortions or errors in that source. It may also add its own interpretation.
This sort of simple example is what the source classification system was intended to deal with. It has, however, been stretched to cover much more complicated situations.
Uses in fields other than history
The initial publication of data from a scientific experiment, such as a clinical trial
, is a primary source.
In science, data is primary, and the first publication of any idea or experimental result is always a primary source. These publications, which may be in peer-reviewed journal articles or in some other form, are often called the primary literature
to differentiate them from unpublished sources. Narrative reviews
, systematic reviews
are considered secondary sources, because they are based on and analyze or interpret
(rather than merely citing or describing) these original experimental reports.
In the fine arts, a work of art is always a primary source. This means that novels, plays, paintings, sculptures, and such are always primary sources. Statements made by or works written by the artists about their artwork might be primary or secondary. Critiques and reviews by art critics are usually considered secondary sources, although exceptions exist. For example, an account of the specific circumstances under which the critic viewed the artwork is primary material, as is the critics' description of their personal emotional reaction to the piece. As a result, some critiques and reviews are a mix of primary and secondary material.
Among genealogists, a primary source comes from a direct witness, a secondary source comes from second-hand information or hearsay
told to others by witnesses, and tertiary sources can represent either
a further link in the chain or
an analysis, summary, or distillation of primary and/or secondary sources. In this system, an elderly woman's description of her wedding day from many decades before is a primary source; her granddaughter's plain repetition of that information to her schoolteacher is considered secondary by genealogists, and if the schoolteacher goes home that evening and writes down what the granddaughter said, then the schoolteacher is producing a tertiary source. In other systems, all of these sources are primary. Genealogists also differentiate between original
documents, accurate copies
(photographs, photocopies or unaltered digital scans) of the original documents, and derivatives (handwritten or re-typed transcripts, digitally enhanced copies, or other methods of copying that might introduce changes or errors). Copies and derivatives retain the same status as the original in the primary-secondary-tertiary classification, unless the derivative is so different as to represent a transformative summary, in which case it becomes a tertiary source.
In some disciplines, notably law, the concept of tertiary sources is not used. In this two-part system, what would typically be classified as a tertiary source by other disciplines is lumped in with secondary sources.
Not a matter of counting the number of links in the chain
Consider the simple example above: the original proclamation is a primary source. Is the book necessarily a secondary source?
The answer is: not always. If the book merely quotes the proclamation (such as re-printing a section in a sidebar or the full text in an appendix, or showing an image of the signature or the official seal
on the proclamation) with no analysis or commentary, then the book is just a newly printed copy of the primary source, rather than being a secondary source. The text and images of the proclamation always remain primary sources.
It's not a matter of counting up the number of sources in a chain. The first published source is always a primary source, but it is possible to have dozens of sources, without having any secondary or tertiary sources. If Alice writes down an idea, and Bob simply quotes her work, and Chris refers to Bob's quotation, and Daisy cites Chris, and so forth, you very likely have a string of primary sources, rather than one primary, one secondary, one tertiary, and all subsequent sources with made-up classification names.
Characteristics of a secondary source
- A secondary source is built from primary sources. Secondary sources are not required to provide you with a bibliography, but you should have some reason to believe that the source is building on the foundation of prior sources rather than starting with all-new material. For example, century-old love letters on display at a museum are primary sources; a secondary source might analyze the contents of these letters. The fact that the analysis is based on these letters would be evident from the description in the source, even if the paper contained no footnotes.
- A secondary source is significantly separated from these primary sources. A reporter's notebook is an (unpublished) primary source, and the news story published by the reporter based on those notes is also a primary source. This is because the sole purpose of the notes in the notebook is to produce the news report. If a journalist later reads dozens of these primary-source news reports and uses those articles to write a book about a major event, then this resulting work is a secondary source. This separation is not defined by the length of time that elapses or geographical distance.
- A secondary source usually provides analysis, commentary, evaluation, context, and interpretation. It is this act of going beyond simple description, and telling us the meaning behind the simple facts, that makes them valuable to Wikipedia.
- Reputable secondary sources are usually based on more than one primary source. High-quality secondary sources often synthesize multiple primary sources, in due proportion to the expert-determined quality of the primary sources. This helps us present the material in due proportion to the sources' actual importance (in other words, assign appropriate WP:WEIGHT), rather than in proportion due to the size of the sources' publicity budgets.
All sources are primary for something
Every source is the primary source for something, whether it be the name of the author, its title, its date of publication, and so forth. For example, no matter what kind of book it is, the copyright page
inside the front of a book is a primary source for the date of the book's publication. Even if the book would normally be considered a secondary source, if the statement that you are using this source to support is the date of its own publication, then you are using that book as a primary source.
More importantly, many high-quality sources contain both primary and secondary material. A textbook might include commentary on the proclamation (which is secondary material) as well as the full text of the proclamation (which is primary material). A peer-reviewed journal article may begin by summarizing a careful selection of previously published works to place the new work in context (which is secondary material) before proceeding into a description of a novel idea (which is primary material). An author might write a book about an event that is mostly a synthesis of primary-source news stories (which is secondary material), but they might add occasional information about personal experiences or new material from recent interviews (which is primary material). The book about love letters might analyze the letters (which is secondary material) and provide a transcription of the letters in an appendix (which is primary material). The work based on previously published sources is probably
a secondary source; the new information is a primary source.
How you use the source affects the classification of the source.