This is an essay on the Verifiability policies. It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints.

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This page in a nutshell: Any material added to Wikipedia must have been published previously by a reliable source. Editors may not add content solely because they believe it is true, nor delete content they believe to be untrue, unless they have verified beforehand with a reliable source.

Wikipedia's core sourcing policy, Wikipedia:Verifiability, previously defined the threshold for inclusion in Wikipedia as "verifiability, not truth". "Verifiability" was used in this context to mean that material added to Wikipedia must have been published previously by a reliable source. Editors may not add information to articles simply because they believe it to be true, nor even if they know it to be true.

The phrase "the threshold for inclusion is verifiability, not truth" meant that verifiability is a necessary condition (a minimum requirement) for the inclusion of material, though it is not a sufficient condition (it may not be enough). Sources must also be appropriate, and must be used carefully, and must be balanced relative to other sources per Wikipedia's policy on due weight.

Wikipedia's articles should be intelligent summaries and reflections of current published knowledge within the relevant fields, an overview of the relevant literature. The Verifiability policy is related to another core content policy, Neutral point of view, which holds that we include all significant views on a subject. Citing reliable sources, for any material challenged or likely to be challenged, gives readers the chance to check for themselves that the most appropriate sources have been used, and used well (see below).

The Verifiability policy was later re-written in 2012 to clarify these points, stating that Wikipedia's "content is determined by previously published information rather than the beliefs or experiences of its editors. Even if you're sure something is true, it must be verifiable before you can add it". That we have rules for the inclusion of material does not mean Wikipedians have no respect for truth and accuracy, just as a court's reliance on rules of evidence does not mean the court does not respect truth. Wikipedia values accuracy, but it requires verifiability. Wikipedia does not try to impose "the truth" on its readers, and does not ask that they trust something just because they read it in Wikipedia. We empower our readers. We don't ask for their blind trust.

Sometimes we know for sure that the reliable sources are in error, but we cannot find replacement sources that are correct. As Douglas Adams wrote of The Hitchhiker's Guide to the Galaxy, "Where it is inaccurate it is at least definitively inaccurate. In cases of major discrepancy it's always reality that's got it wrong."

Prior to July 2012, the policy read, "The threshold for inclusion in Wikipedia is verifiability, not truth." Written more verbosely, this means "The threshold for inclusion in Wikipedia is verifiability. The threshold for inclusion in Wikipedia is not truth."

• Threshold: This word has multiple meanings, and the relevant one is "The point at which an action is triggered, especially a lower limit." This means the absolute minimum standard for including information in Wikipedia is verifiability. If the information is not verifiable, you must not include it under any circumstances. Merely meeting the absolute minimum standard for inclusion is not sufficient. Material may be verifiable, but still banned by several other content policies, including Wikipedia:Neutral point of view, Wikipedia:Copyright violations, Wikipedia:What Wikipedia is not, Wikipedia:Biographies of living persons, and by editorial judgment about whether this article is an appropriate place for presenting that information.
• Verifiability: In Wikipedia's sense, material is verifiable if it can be directly supported by at least one reliable published source. Verifiability is not determined by whether the material has already been supplied with an inline citation.
• Not truth: It is not good enough for information to be true, and it is definitely not good enough for you to (perhaps wrongly) believe it to be true. Wikipedia values accuracy, but it requires verifiability. You are allowed and encouraged to add material that is verifiable and true; you are absolutely prohibited from adding any material that is un-verifiable, with zero exceptions—even if the un-verifiable material is True™.

This policy was then re-written in July 2012 to clarify these principles, but the core message remains the same: Any material added to Wikipedia must have been published previously by a reliable source. Unless you have verified it beforehand with a reliable source, you may not add content just because you believe it is true, nor may you delete content that you may believe to be untrue.

Fact, truth and Truth

Truth has two meanings that are not always separated:

• that which is in accordance with fact, and
• a fact or belief that is accepted as true.

Facts established by inquiry, or a verifiably accurate statement is the meaning of truth normally used by the natural sciences and in legal contexts. This first kind of true statement may not accord with facts, but it does accord with the facts as they are currently understood, even though there is a chance that the scientific idea might eventually become obsolete, or that other evidence might appear in a lawsuit.

The second meaning – something believed to be true – is used in religion, moral philosophy, and many everyday matters, such as when you genuinely believe that you turned off the oven after taking out the pie, but you decide against getting up to verify your belief, or when everyone agrees that this summer's big teen film was even worse than the usual (low) standards for that genre. You might be wrong – your religious beliefs might be incorrect, your philosophy might be misguided, the oven might still be turned on, and the film might be better than you thought it was – but when you make these claims, you are speaking with a genuine, honest belief in your statement.

The word fact, in its modern meaning, is a statement that is consistent with empirically established reality or proven with evidence. This meaning is actually relatively new. Its genesis is the Latin factum, a thing which is done. In law, the fact was originally the crime, so an accessory after the fact assisted the criminal after the commission of the act; this developed into something closer to the modern meaning – just the facts, ma'am. From the middle of the 16th century it began to be more generally used to describe a thing that was testably true, and this usage is inextricably linked to the development of the scientific method. The scientific revolution replaced eternal Truths, taught didactically, with experimental verifiability as exemplified by the motto of the Royal Society: nullius in verba, take nobody's word for it. The Truth that heavier objects fall faster than light ones, taught by Aristotelians for over a thousand years, was blown away in a few decades by experiments that show it not to be true.

Many long and bitter edit wars have had their genesis in the difference between the two types of truth – truth versus Truth. Wikipedia policies mandate that we describe the latter while reflecting the former. Hence we write articles from the perspective that the Earth is, objectively, 4.5 billion years old, while describing the common beliefs in much younger ages, in contexts where this is relevant. The era of post-truth politics is, in fact, a resurgence of the pre-fact period. While there will be one verifiable and objective "truth", there can be many versions of subjectively believed "Truth", and whose "Truth" gets to win here?

"Truth" has a tendency to be subjective, so there will be disagreement over whose version of "truth" is factual and can be included here. Here we prioritize facts over subjective truths. If a truth is verifiably and demonstrably real, we often describe it as "fact":

In our time, it can be argued that the burden long borne by the word truth has shifted to the word fact. If truth has come to be regarded as subjective – the realm of the personal – we still see reasonable people of widely disparate backgrounds recognizing facts for what they are. They are the building blocks of demonstrable reality. They are the beyond denial, beyond the debate on competing cable TV news channels.^[1]

Because truth is not always something as clear and unquestionable as we may desire. In many cases, such as in many questions related to social sciences, there is no "truth" but simply opinions and assumptions. Which is the best political system? Was this or that government a good or bad one? There are no "true" answers to such questions, without rigorously defining and agreeing on the terms (what does it mean, in exact detail, defined as an objective standard, for a government to be "good"?). Instead, there are facts, opinions, facts about opinions, and opinions about opinions. We must not present a fact as an opinion, nor an opinion as a fact; and so on for the other categories.

Besides, truth is a boolean value (100% true or 100% false) only in certain technical contexts, such as mathematics or programming languages. In most other contexts, there are more than truths and lies under the sun: there are half-truths, lack of context, words with double or unclear meanings, logical fallacies, cherry-picked pieces of information to lead the reader to a predetermined conclusion, inadvertent reuse of someone else's lies, and even misunderstandings. A statement may fail to adequately convey the state of affairs regarding some topic, without that statement being an actual lie.

In other cases, accuracy itself is under dispute: a certain question may indeed have a true answer, but nobody knows what it is yet, so a lack of complete information leads to people supporting a variety of possible answers. For example, the existence of extraterrestrial civilizations, or the existence of life on Europa, could be true or false. There is indeed a factual answer (either there are extraterrestrial civilizations, or there are not), but we are not 100% certain of it.

Are you sure that's the case? Many times, when everybody considers something to be one way but you find somewhere else that "everybody is mistaken" and things were actually some other way, it's more likely you have found a fringe theory. The stance of Wikipedia on such things is to avoid giving undue weight to such minority ideas, and represent instead the current state of understanding of a topic. If there's indeed an accuracy dispute between scholars, it is described without taking part. If there's an almost universally accepted viewpoint and a tiny minority one, the minority opinion may be ignored in favor of the viewpoint held by the majority, and the majority viewpoint will be described as fact.

However, representing a majority viewpoint as such does not equal considering it true, and it is possible that "everybody" is indeed actually mistaken. For example, before Pasteur, everybody considered the spontaneous generation theory to be true, and they were mistaken. Even so, if Wikipedia had existed before Pasteur, it would have treated it as an accepted theory because the majority of experts (scientists in the relevant fields) thought it was true.

And in this hypothetical scenario, what if Pasteur fixed the article on spontaneous generation after proving it was wrong? Because he was using his own original research, thus making Wikipedia into a primary source, Wikipedia couldn't have accepted it. Wikipedia does not know, nor does it have the resources to verify, if either one is correct or incorrect, or to set apart an unpublished but revolutionary theory from a common fringe one. That's why it relies on verifiability rather than truth. Pasteur would have been required to explain his theory in the regular scientific field, and have it checked and approved by peers. Only then would Wikipedia add changes concerning his discovery. Wikipedia only reports what the reliable sources say; it does not publish what its editors just believe is true.

In many cases, if something appears in a reliable source, it may be used and attributed where needed, but reliable sources are not infallible. There are examples where material should not be reported in Wikipedia's voice, because what is verifiable is that the source expresses a view, not that the view is necessarily accurate.

• Most sources do not state their opinions as opinions, but as facts: we are more likely to find "The hypnotoad is supreme" than "Our opinion is that the hypnotoad is supreme, but there are others who disagree with us." It is the task of the Wikipedia editor to present opinions as opinions, not as facts stated in Wikipedia's voice; this is one reason Wikipedia's voice should be neutral. The best way to describe a dispute is to work with a tertiary source that already describes the dispute and cite it as a reference. Tertiary sources may also help to confirm that there is a legitimate dispute to begin with, and not just a fringe theory against a universally accepted idea.
• It is important not to "cherry-pick" quotations or other material. Source material should be summarized in context to make sure it is represented fairly and accurately, and undue weight should be avoided.
• In some cases, publication in a reliable source is not sufficient to establish that a view is significant. Reliable sources may be outdated or disputed by other sources. Books from before Pasteur would state the theory of spontaneous generation to be a fact; they are still useful sources to explain that theory, but not to describe the modern state of knowledge on the topic. There are a few immortal authors whose works are never outdated, but they are rare. Even books just a few years old may be missing new, important information.^[2] In fact, because a book requires time to be edited and printed, in rare cases it may already be out of date when it is first released.
• Reliable sources may express speculation, or a source for a significant view may include in it views that are not significant. In these cases, criteria other than those described in our policy on sources are necessary.
• Even the most reliable sources commit mistakes from time to time, such as misspelling a name or getting some detail wrong. Such mistakes, when found, should be ignored, and not be employed to describe a non-existent dispute. To know where we have a dispute and where a simple mistake, consider whenever the author is really an expert on the topic (and not an expert on another topic, making a brief reference to something beyond their area of expertise), or if the text that breaks the mainstream knowledge is provided on purpose or as a mere passing-by comment. For example: George Washington was born in 1732. Let's consider a tour guide who says, "Washington, D.C., is the capital of the United States, and it's named after George Washington (1722–1799), the first president ...", then that's just a mistake. But if we have an article written by some famed historian, stating something like "New historical evidence would date the birth of George Washington to 1722, ten years before it was usually known", then it would be a different thing ... regardless of whether such a hypothetical claim was true or not.
• Just because it looks like a mistake, doesn't mean the source is mistaken. Many sources say George Washington was born in 1732 on the 11th of February, whereas many more-modern sources say he was born in 1732 on the 22nd of February (some say both). The two dates are both 100% correct. The sources just rely on differing date-keeping systems (Julian calendar versus Gregorian calendar); the changeover happened in the British Colonies during the 1750s, when Washington was a young adult. See the first sentence of George Washington for how to deal with conflicting sources properly.
• Works of fiction about real historical peoples or events must never be used as sources for historical fact, no matter how accurate they may be. Fiction needs to have a beginning, a chain of events, an ending, well-defined characters, etc.; something that reality rarely has. Even more, they may need to twist things for narrative purposes, or add new features where the original lacks them. So, if you want to write an article about Eva Perón, do not use Madonna's film as a source. If you want to edit the Battle of Thermopylae article, do not use 300 as a source. However, they may be used as primary sources to describe the plot of such works of fiction.

Wikipedia doesn't reproduce verbatim text from other sources. Rather, it summarizes content that some editor(s) believes should belong in the Wikipedia article in the form of an encyclopedic summary that is verifiable from reliable sources. This process involves editors who are not making claims that they have found truth, but that they have found someone else who is making claims that they have found truth. If there is more than one set of facts or explanations for the facts in the article, there's a guideline for that where multiple points of view (Wikipedia's term for versions of truth) are included.

Wikipedia editors are not indifferent to truth, but as a collaborative project written primarily by amateurs, its editors are not making judgments as to what is true and what is false, but what can be verified in a reliable source and otherwise belongs in Wikipedia.

If editors come upon some information which seems dubious, and it is supported only by dated sources, looking for more modern sources which contain updated information, if they have access to such sources, is preferable to removing the inaccurate material immediately, unless they have good reasons to do so.

Logic and mathematics

The field of mathematics is strongly based in logic; most, but not all, mathematical operations provide statements whose truth, falsehood, or unknowability is beyond dispute under certain assumptions of axiomatic consistency. 2 + 2 = 4 is true under Peano's postulates (if the latter are assumed to be consistent, which cannot be proven), as is 2⁸ = 256. 2 + 2 = 5 is false under these assumptions. The value of Chaitin's constant Ω is unknowable.

There are many other sciences that make extensive use of mathematics, such as most formal sciences and physical sciences. The same rule applies to them, as far as it is based only on basic mathematics. Statements beyond mere calculations, such as proposed theories, must be described, cited and attributed as anything else.

Natural sciences

By "natural science" is here meant a science such as geology, anatomy, or physics. In natural sciences, there is a degree of factuality that is hard to dispute, as well as more disputable attempts at factuality. Besides factuality, natural sciences also have conventions or customs, and speculation and opinion. Consequently, some judgment and comparison of sources is needed in order to identify reliable sources. Reliable sources respect truth; a source that is commonly untruthful is not reliable. A source may be partly or more or less reliable. Concurrence of possibly reliable sources may help in identifying reliable sources, and editors should seek it. Conflict between truth as a criterion and reliable sourcing as a criterion may nevertheless be a matter of opinion. Reliable sourcing and truth ought to coincide, at least to some degree; such is to be sought by Wikipedia editors. Wikipedia should avoid untruth, even if it appears in otherwise apparently nearly reliable sources. Only reliably sourced material should be posted in Wikipedia articles.

Social sciences

There are fewer universal facts in social sciences (and none at all in some fields). History has more facts than sociology, and psychology has more facts than political science; regardless, as said earlier, we must distinguish between facts, opinions, facts about opinions, and opinions about opinions. Only facts (including facts about opinions, but not the opinions themselves) have a truth value, and even then, it's much less clear than for mathematics and logic. For example, "The administration of president 'Whoever' promoted the slogan 'resistance is futile'" is a fact. But there are many things to consider before one can have a complete understanding of the topic: What was the context? Who supported promotion of the slogan? Who opposed it? What was the reception among society? Which events motivated it? What were the results? The omission of such context can itself make something seem better or worse than it really was.

As history is about things that took place in the past, there's a temptation to think it is composed entirely of truths. It isn't. History is the politics of the past, just as today's politics is tomorrow's history. While historical facts certainly exist (like the fact that World War II occurred), the opinions and perspectives about the presidency of Abraham Lincoln or Richard Nixon are as diverse as they are about Barack Obama or Donald Trump.

Fictional topics

Articles about works of fiction have two different perspectives that should be considered. First, the real-world perspective about the creation and reception of the work of fiction. In this perspective, which must not be omitted, "truths" are as relative as for social sciences. We have facts, like dates of publication; opinions, like information about any meaning or message contained in the work; facts about opinions, like who believes the work has a certain meaning; and opinions about opinions, like beliefs about people who believe the work has a certain meaning.

The second perspective is the plot. Highly complex fictional works aren't just limited to creating characters, but also fictional universes, fictional technologies, fictional artifacts, perhaps even fictional scientific laws or phenomena (such as the Force from Star Wars). For any information beyond a direct description of the work's contents, it is tempting for fans to see things from here and there, draw connections, relate things and draw conclusions, but that is original research. Where one fan arrives at a conclusion, another fan takes other details and arrives to the opposite one. So, the truth on questions such as "Who would win, the Hulk or the Thing?" is the boring but accurate "Whomever the writer decides according to the narrative of the story."

When there are many different stories set in a same fictional universe, it is usually desirable to have a good continuity among them. However, it is important to remember that continuity is a consequence, not a preexisting condition. If two episodes, movies in a saga or comic books say contradictory things, then the "truth" is simply that they said contradictory things, and a good continuity was not achieved. It is not acceptable to seek details from here and there and make up an explanation so everything fits in place.

This phrase was originally added to Wikipedia:No original research as a summary of the Verifiability policy in March 2005. It was coined on 8 December 2004 during a months-long discussion of a draft to improve the policy on original research. The phrase with its explanation was moved to the Verifiability policy in August 2005. It remained in both policies until July 2012, when the phrase was dropped following a 30-day discussion. It still remains in WP:V in a footnote with a link to this essay.

• Verifiability, not truth in action, a real example on Wikipedia of this ideology being used
• Wikipedia:Truth matters
• Wikipedia:Amnesia test
• Wikipedia:No original research
• Wikipedia:Otto Middleton (or why newspapers are dubious sources)
• Wikipedia:Truth, not verifiability
• Wikipedia:Verifiability
• Wikipedia:Correct
• Wikipedia:Accuracy
• Wikipedia:The Truth
• Wikipedia:Verifiable but not false, an essay on limiting false information on Wikipedia