Wikipedia:Identifying and using tertiary sources: Difference between revisions

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{{Essay|interprets=[[WPWikipedia:No original research]], and [[WPWikipedia:Identifying reliable sources]]|cat=Wikipedia essays on reliable sourcesWP:TERTIARYUSE|shortcut=WP:TERTIARYUSEUSETERTIARY}}

{{nutshell|1=Analysis and evaluation require reliable secondary sources, and we cannot cite tertiary sources for them. Tertiary sources differ from secondary ones by not themselves providing significant analysis, commentary, or synthesis. However, some tertiary sources are secondary in some applications.}}

Generally speaking, [[tertiary source]]s (for Wikipedia purposes, as discussed at {{section link|WPWikipedia:No original research|Primary, secondary and tertiary sources}}, and {{Section link|WPWikipedia:Identifying reliable sources|Primary, secondary, and tertiary sources}}) include any compilation of information, without significant new analysis, commentary, or synthesis, from primary and secondary sources, especially when it does not indicate from which sources specific facts were drawn. The distinction between tertiary and [[secondary source]]s is important, because Wikipedia's [[WPWikipedia:No original research|no original research]] policy states: "Articles ''may'' make an analytic, evaluative, interpretive, or evaluativesynthetic claim ''{{em|only if''}} that has been published by a reliable secondary source." Thus, such claims cannot be cited to tertiary or [[primary source]]s.

== Identifying ==

{{shortcut|WP:IDTERTIARY}}

There are many types of {{em|typically}} tertiary sources:

* [[Encyclopedia]]s, [[Dictionary|dictionaries]], [[Encyclopedic dictionary|encyclopedic dictionaries]], and [[Compendium|compendia]], (whether general or topical). These are often, but not always, high-quality and reliable sources (compendia are the least likely to be acceptable).

* [[Coffee table book]]s run the gamut from books written by experts and published by internationally renowned museums, to books filled with photographs of a particular place or subject, on down to books whose sole ''raison d'être'' is making people laugh.

* "[[Coffee table book]]s" and [https://www.goodreads.com/list/show/6486.Best_Bathroom_Books "bathroomBathroom books"]. These are usually low-quality sources and presumptivelyshould usually be unreliableavoided.

* School [[textbooks]], especially below the graduate-school level. If they are below the university level, they are treated as categorically unreliable by Wikipedia.

* School [[textbooks]], especially below the university level in the natural sciences and below the graduate-school level in some other fields.

* [[Bibliographies|Bibliographies]] and [[Bibliographic index|indexes]], [[Concordance (publishing)|concordances]], [[Thesaurus|thesauri]], [[database]]s, [[almanac]]s, [[guide book|travel guides]], [[field guide]]s, [[timelines]], and similar works. Quality varies widely.

* [[Abstract (summary)|Abstracts]] of journal articles, legislation, etc., provided by indexing services and specialized search engines (not abstracts written by the article authors themselves). Low-quality sources. May be reliable enough for basics in some cases, depending on reputability of the publisher. The abstract included atop a journal article and written by its own authors is a primary, not tertiary source.

Some of the above kinds of tertiary sources are considered forms of [[secondary literature]] in some disciplines, but {{em|remain tertiary}} (for most of their content) for Wikipedia's purposes including in those disciplines. Not understanding this is a common error by subject-matter experts new to Wikipedia editing.

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The medium is not the message; source evaluation is an evaluation of content, not publication format.

* Sometimes high-quality, generally tertiary individual sources are also primary or secondary sources for some material. Two examples are etymological research that is the original work of a dictionary's staff (primary); and analytical not just regurgitative material in a topical encyclopedia written by a subject-matter expert (secondary).

* Material found in university textbooks ranges from secondary to tertiary, even in the same work, but is most often tertiary, especially at lower levels and covering more basic subjects. Textbooks intended for primary and secondary schools are almost always tertiary and, for Wikipedia purposes, categoricallyreliable only for uncontentious basic unreliablematerial.

* Children's books of any kind are tertiary at best, often primary, and categoricallyare usually unreliable sources. Especially beware citations to books about animals; the majority of them are children's books, so check to be sure. In the same [[Wikipedia:Children's, adult new reader, and large-print sources questionable on reliability|class of suspect works]] are "adult new reader" books, and abridged large-print editions, or any other digest version.

* Some material published in general [[Journalism|news and journalism sources]] (which are [[WP:PRIMARYNEWS|usually secondaryprimary]]) is actually tertiary, such as topical [[overview article]]s that summarize publicly-available information without adding any investigation or analysis; and sidebars of statistics or other [[factoid]]s in an otherwise secondary article. (Some is also primary, such as editorials, op-eds, film reviews, advice columns, and highly subjective investigative journalism pieces.) News reporting is often mostly primary (quoting eyewitness statements, or the observations of an eyewitness reporter, rather than based on more in-depth material from experts and notable organizations). NewNews reporting is treated more and more {{em|as if}} primary, regardless of what it contains, the closer it is to the date of the events, and the further in time those events recede.

* Similarly, not all [[Documentary film|documentaries]] aired on quasi-nonfictional TV networks are actually secondary sources; many are tertiary, and simply summarize various views of and facts about a history or science topic, without the result being novel. Some are even primary, for any exaggeratory conclusions they reach on their own. This has become increasingly true as documentary channels produce more [[WP:FRINGE|fringe]] entertainment material about aliens, ghosts, ancient alleged mysteries, etc.

* [[Systematic review]]s in [[academic journal]]s are secondary sources, especially when they are themselves [[Peer review|peer-reviewed]], despite aggregating information from multiple previous publications. The less analytic kind of academic [[review article]], the [[literature review]], may be secondary or tertiary depending on its content.

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Tertiary online sources that are written in whole or in part by a general-public editing community are [[WP:Identifying reliable sources#User-generated content|user-generated content]], and are not reliable sources. This includes [[content farm]]s, which have a paid but indiscriminate array of innumerable writers, and little editorial oversight, though many of them go to some lengths to disguise their nature.

== Appropriate and inapppropriateinappropriate uses ==

{{shortcut|WP:USETERTIARY}}

=== Usually acceptable uses ===

'''Simple facts:''' A tertiary source is most often used for reference citations for basic and fairly trivial facts thatwhich are not likely to be disputed and which can be verified in other sources. Examples include various vernacular names for a species, the pronunciation of a foreign word, or a baseball player's statistics in a particular year. The [[WP:Good article nominations]] and [[WP:Featured article candidates]] processes tend to check that {{em|all}} statements in an article are sourced, and tertiary sources frequently are used for many non-controversial details.

'''Simple comparisons:''' Another common use is comparative, especially involving simple facts and basic concepts. An example is citing multiple dictionaries to show how interpretation of a term may vary. (Comparative use of tertiary sources for more complex or contentious material is ill-advised, as detailed below.)

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'''Better than nothing:''' Tertiary sources are also commonly used when a secondary source has not yet been found. For example, a field guide about cacti has probably been reasonably well fact-checked, and can be cited as a source for the range of a particular species, if no source focusing on that species (and perhaps with more recent data) has turned up yet.

'''Older but still relevant details:''' Older tertiary sources can be used to source former, obsolete views or facts that need to be reported on in a Wikipedia article, for completeness, especially when it's difficult to find modern sources that even mention a long-replaced idea, name, person fulfilling a role, or whatever. As detailed below, there is a major difference between using a tertiary source to report obsolete facts as such, and trying to use them to preserve obsolete facts as still verifiable (e.g., you can use 19th-century encyclopedias to illustrate how seriously [[phrenology]] was once taken, but such sources cannot be used to try to contradict modern scientific works).

=== Problematic uses ===

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'''Analysis and evaluation:''' A tertiary source cannot be used, as a matter of policy, as a source for "an analytic or evaluative claim". This is left deliberately broad, so it is not subject to [[Wikipedia:Gaming the system|technicality gaming]].

'''Controversial material:''' Any controversial, alleged fact is essentially unsourced if the only citation it has is to a tertiary source of questionable reliability (on the particular point or generally). As with secondary sources, this can happen for any number of reasons, including source obsolescence, lack of subject-matter expertise, conflict of interest, simple error, or presentation of a [[WP:FRINGE|fringe]] idea as comparable to the generally accepted view, among other problems that can arise with a particular source. A tertiary source that is a compendium of factoids by an author with no known expertise, and which indicates nothing about the sources of its own information, is not a reliable source. Anyone could compile a large book of alleged facts, anecdotes, and folklore about any given topic, and probably find a willing publisher, without any fact-checking ever taking place. Note however that not all facts about a controversial subject are themselves controversial; there is no principle that a reliable tertiary source good enough for one article is not good enough for another because of the topic's notoriety, the amount of emotion editors bring to editing it, or the frequency with which our article on it is vandalized.

'''Complex or controversial comparisons:''' Comparative use of tertiary sources can be fraught with problems relating to [[WP:Undue weight|undue weight]], [[WP:Neutral point of view|non-neutral point of view]], [[WP:SYNTH|novel synthesis]], and lack of basic [[WP:Verifiability|accuracy]] if the things being compared are subject to real-world contention, or are complex in nature. For example, a comparison between Christian, Judaic, and Muslim concepts of God is unlikely to produce encyclopedic results if based in whole or part on tertiary sources, which are likely to present a poorly nuanced view of complex theological questions and details of interpretation. Complex comparative work must actually be done in secondary sources cited by Wikipedia for those comparisons. The [[WP:AEIS]] policy does not permit Wikipedians themselves to engage in substantive "analysis, evaluation, interpretation, or synthesis" of facts or sources.

'''Over-inclusive works:''' [[WP:Independent sources#Indiscriminate sources|Indiscriminate sources]] must be considered skeptically when determining both [[WP:Notability|notability]] and [[WP:Undue weight|due weight]]. Unfortunately, a large proportion of tertiary sources are indiscriminate. A guidebook that attempts to describe every restaurant in a city cannot reasonably help establish that a particular restaurant is notable. An index of every paper published about a topic in a given year tells us nothing about the critical reception of any given paper. The more inclusive, comprehensive, even "complete" that a work aims to be, the less useful it is for determining the notability of any subject it mentions. On the up side, the more comprehensive a work is, the more likely Wikipedia editors are to find reliable details in it about any subject within its purview. Thus, in a selection of tertiary sources for a topic, the source that is most reliable for [[WP:Verifiability]] purposes has a tendency to be the least valuable for notability and due weight analysis. The inverse is often not true; an exclusively selective, non-comprehensive source may well be very unreliable, too, simply because it was poorly researched and reflects a superficial, popular-opinion approach to its topic, as is often the case with coffee table books.

'''Better sources available:''' While a good tertiary source can usually be used without incident to source non-controversial facts, such citations can and should be superseded by ones to reliable secondary sources. [[WP:Identifying reliable sources]] tell us: "Each source must be carefully weighed to judge whether it is reliable for the statement being made and is the best such source for that context." It is extremely rare for a tertiary source to be the best such source, for anything, in any context; they're simply often the most readily available and easily digestible (being somewhat predigested). Sometimes a tertiary source can even be replaced with a primary one; for example, a dog breed's actual breed standard (the primary source) is more reliable for the breed's defined characteristics than a tertiary dog breed encyclopedia, though the latter might be very useful for differences and commonalities between varying standards published by different organizations, and may be a good source of additional details, like demographics and breed history. "Stacking" tertiary source citations after a sufficient secondary one [[WP:OVERCITE|is not advised]]; it does not add more verifiability to the claim in the article, but simply adds clutter.

'''Outdated material:''' An obsolete source cannot be used to "trump" newer reliable sources that present updated information, most especially when the older source states or implies a negative that cannot be proven but can be disproven easily by new data. A pertinent example (detailed [[Wikipedia:Inaccuracy#Examples of verifiable yet potentially inaccurate material|here]]) is a prominent dictionary asserting that a specific phrase was first used in publication in a certain year, while later research found older examples, disproving this assertion (with its implicit negative, that there were no earlier cases). Because most tertiary works take a long time to assemble, or (in more dynamic media) are in a constant state of being incrementally updated, it is fairly likely that some particular pieces of information in such a work have already been surpassed by the newer work of others. Some information in tertiary sources may already be obsolete before they even see publication. Sometimes the very conceptual framework behind such a work becomes obsolete, given the passage of enough time, with enough advancement and reorganization in the field to which it pertains. E.g., ana decades-old tertiary list of species within a genus, based on outmoded ideas of classification, cannot be used to contradict or seek undue weight against a widely accepted re-classification arrived at through more modern research. On the other hand, a recent high-quality tertiary source with clear and reliable sources may be of more value than an obsolete secondary one, especially in the sciences, where current understanding can be a fast-moving target.

== See also ==

* [[WP:No original research]] (policy)

* [[WP:VerifiabiltyVerifiability]] (policy)

* [[WP:Identifying reliable sources]] (guideline)

* [[WP:Identifying and using independent sources]] (essay; how to identify when a source may be biased due to a connection to its subject)

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* [[Template:Tertiary source inline]] (used outside {{tag|ref}})

* [[Template:Tertiary source]] (used inside {{tag|ref}})

{{Wikipedia essays}}

[[Category:Wikipedia essays about reliable sources]]