Wikipedia talk:Common knowledge

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Note: User:Beland moved the following discussion here on March 12 from Wikipedia talk:Reliable sources. Nothing before this timestamp was written with this page in mind. SlimVirgin 03:53, Mar 12, 2005 (UTC)

Semi-common knowledge[edit]

Beland, this is extensive, and I've only glanced at part, but ... Can you clarify whether this allows for material that is not known to be published but is common knowledge and undisputed among people with at least moderate knowledge of the subject? Maurreen 09:02, 5 Mar 2005 (UTC)

Maurreen, you have identified the grey area. Some knowledge is so obvious that it requires no proof in sources (e.g. the Sun rises in the East). Yet, for me it is obvious that high levels of parathyroid hormone cause hypercalcemia (elevated blood calcium levels), while others would like to see proof that I'm not making this up. While this is probably undisputed, it is falsifiable due to the (relative or potential) ignorance of the readership. JFW | T@lk 01:21, 6 Mar 2005 (UTC)
Does this mean we have a consensus to keep it gray? :)
Maybe we should just have a sentence somewhere along the lines of "Material which is undisputed should not be removed solely because a source is not identified"? Maurreen 01:29, 6 Mar 2005 (UTC)
I didn't intend for this page to encourage anyone to remove anything; what to actually do when you find an undocumented fact or unreliable source is the question that's being hashed out at Wikipedia:Confirm queried sources right now. -- Beland 01:56, 6 Mar 2005 (UTC)
Everything is allowed, of course, but as for what's recommended as the most reliable...
There's a distinction between facts that one can personally verify and facts that everyone who is moderately familiar with a particular area "knows". For the second kind of "facts", I would recommend seeking reliable published sources or people with personal experience who can serve as primary sources. If no such sources exist, you could either report the statements as widely believed but unverified, or be more specific and reference "less reliable" sources and characterize their reports as unverified or speculative. Even in scholarly communities, it's easy for something to become "widely known" without actually being true. But on the scale of reliability, there are worse things.
If this isn't clear from the front page, maybe it needs to be improved. -- Beland 01:51, 6 Mar 2005 (UTC)
I was thinking of facts that one can personally verify. But no biggie either way. Maurreen 01:53, 6 Mar 2005 (UTC)
Beland, I hadn't looked at your most recent changes. I think that clarifies the matter well. Thanks. Maurreen 01:55, 6 Mar 2005 (UTC)

Common knowledge[edit]

I find the "Common knowledge" section troubling. For example, it says

Wikipedians have should have direct personal knowledge of the facts reported. This does not include hearsay - hearing or reading about something or even learning about something in school. (See the above section "Hearsay".) For those things, you (or someone else) should be able to cite a reliable source.

If someone says "I was there and I saw it", how can we evaluate this claim? Perhaps the person is telling the truth, perhaps lying, perhaps his memory is terrible, perhaps he was hallucinating.

You should evaluate them like you would any other primary source. The author of a famous book could easily also have any of these faults. For some things, having a real live person with an eyewitness account you can communicate with and ask to clarify their statements and whatnot, is certainly better than reading an eyewitness account. And getting several eyewitnesses to different instances of the same phenomena to agree is often an even better verification. But it depends on the subject matter. -- Beland 03:10, 12 Mar 2005 (UTC)

I also find this sentence difficult:

No particular technical expertise should be required to understand or verify "common knowledge" facts.

Many proponents of crackpot theories insist that no particular expertise is required to understand or verify their theories. As examples, how would you deal with people who made the following assertions as "common knowledge"

"The Jewish lobby controls American foreign policy, especially as regards Israel".
"The Israeli settlements are illegal under international law".

Are these statements acceptable in Wikipedia articles as "common knowledge"? Jayjg (talk) 03:27, 11 Mar 2005 (UTC)

I would say that these are both statements on a subject about which there is a significant amount of known controversy, so whether or not one has or needs legal expertise to understand these statements is not a necessary question to decide. Though in general, I would not recommend applying "common knowledge" verification to any legal subject. If something is illegal, there should be plenty of written evidence which is more authoritative than the testimony of a random person off the street. This is another reason not to use "common knowledge" verification for the second statement. People are also perfectly free to say, "I don't agree. I think the opposite is true." If there's no rough consensus, then a claim based on "common knowledge" grounds should be removed. -- Beland 03:10, 12 Mar 2005 (UTC)
I tried to copy edit the Common knowledge section in line with Jay's concerns, but found that it all seemed to contradict Wikipedia:No original research, so I deleted it. It's "common knowledge" that we're trying to keep out of Wikipedia. Everything must be verifiable with reference to credible, published sources. That doesn't mean that a reference has to be provided for every single claim, but there should nevertheless be references available if an editor challenges an edit, and if none are available, any editor may delete the claim. Also, there are a few references to incorrect facts, or "facts, true or false." There's no such thing as an untrue, false, or incorrect fact. A fact is an actual state of affairs, true by definition. SlimVirgin 02:15, Mar 12, 2005 (UTC)
I reincarnated the section as it own page here, so we can discuss it separately from Wikipedia:Reliable sources. -- Beland 03:10, 12 Mar 2005 (UTC)

Based on the above comments, I will try a quick re-write to express the points I was trying to make in a clearer, more comprehensive fashion. -- Beland 03:10, 12 Mar 2005 (UTC)

Too many new pages and talk pages[edit]

Note: Beland just moved all of the above over from Wikipedia talk:Reliable sources. but I have copied it back as there is an ongoing discussion there, and other editors have been checking the page and commenting elsewhere. This situation is becoming very confusing, and I would say not helpful. These are important policy or guideline changes that are being discussed, yet the discussions are taking place on the talk pages of Wikipedia:No original research, Wikipedia:Cite sources, Wikipedia:Reliable sources, the oddly named Wikipedia:Confirm queried sources, and now Wikipedia:Common knowledge, and perhaps elsewhere too. This spreading around of the discussion means editors won't be able to keep track of the issues, so that pages will be created or altered with little consensus, and therefore will be changed back again. Also, it means contradictions may creep in: for example, there was material in Wikipedia:Reliable sources that seemed inconsistent with Wikipedia:No original research and Wikipedia:Cite sources. SlimVirgin 03:53, Mar 12, 2005 (UTC)

Beland, this page has to go. It completely contradicts policy. NOR is policy, not just a guideline. It also contradicts Wikipedia:Cite sources and Wikipedia:Reliable sources. I don't understand what you are trying to achieve here. SlimVirgin 03:53, Mar 12, 2005 (UTC)

Why this page was created[edit]

I created this page because it seemed like Wikipedia:Reliable sources was going to relatively easily reach consensus, but that this section was controversial. I pondered creating them separately in the first place, but I thought hey, maybe they're closely enough related that they belong in the same place. I separated them recently because it seemed that we were in danger of discussing two different chunks, each of very different quality, on the same page, and I was afraid that would be too confusing. I guess there's danger of confusion no matter which way I do things.

Both articles are in Category:Wikipedia policy thinktank. This is a place where ideas that are not (or are not yet) "blessed" policy get hashed out.

I agree that as ideas mature, it's good to reconcile contradictions, and that page mergers can be a good way to do that. But these things take time. I would expect this type of idea to remain in the thinktank for at least 30 days before moving up even to Category:Wikipedia semi-policy. Perhaps at this milestone, there should be some sort of vote that's broadly advertised. But in the meantime, it's good to discuss and criticize and improve, so that we can try to form a broad agreement on the best language on which to take a vote.

We have plenty of pages for proposals that contravene existing policy. They should be clearly marked as non-policy, but kept around so there's a record of not only what we decide, but what we decide against. See, for example, Category:Wikipedia rejected policies. -- Beland 05:23, 12 Mar 2005 (UTC)


More discussion on "common knowledge" continues on Wikipedia talk:Reliable sources. -- Beland 05:24, 12 Mar 2005 (UTC)

I think this page is fine[edit]

That's all. Maurreen 07:34, 12 Mar 2005 (UTC)

Common usage of words in a foreign language[edit]

See Talk:Antipodes#Antipodes as a European term??? : The problem of proving the common usage in a language to a person that is unable to speak it is challenging and interesting in itself, as the combination makes it very hard to strictly comply with WP:Source. Would anybody like to comment on how to address the question? Sergio Ballestrero 00:15, 7 May 2006 (UTC)

I'd say that, if the language is widely enough spoken that we can suppose a reasonable audience of present & future Wikipedia editors with some exposure to it, it would be out of line to challenge the content too urgently. "Delete if not verified" applies to insidious or surprising material, POV material, contributions from probelmatic editors. But if there's a large audience of people more knowledgeable than yourself, I'd say let it stand unless the complaint comes from them. WP:RD/L is a pretty fast place to get information about what is undisputed in many of the world's languages. Wareh 03:33, 17 October 2006 (UTC)

Historical "Facts"[edit]

As a professional historian I'm a bit troubled by this interpretation:

  • Historical facts. If none of the current editors were alive when it happened, then a contemporary written account, or the account of a professional historian, is likely to be considerably more accurate.

On the one hand, first hand observation smacks a bit of original research. I know first hand that when it first came out Thomas Kuhn's The Structure of Scientific Revolutions was assigned in university courses in a wide range of disciplines. That point would fit very well in that article, but I have no intention of adding it.

Secondly, since Wikipedia prefers secondary to primary sources, I would put the account of a professional historian before a contemporary written account. As Jimbo recognized [1][2] interpretation of primary historical sources requires experience. When I moved from being a physics major to being a historian, it took about three semesters to get the hang of it.

I'd suggest replacing it with the following:

  • Historical facts. An account of a professional historian, or if none is available, a contemporary written account. In the latter case, such a primary source should be interpreted with caution. —The preceding unsigned comment was added by SteveMcCluskey (talkcontribs) 20:03, 23 August 2006 (UTC)

Since no one's objected, I've made the proposed change. --SteveMcCluskey 20:46, 26 August 2006 (UTC)

Is this a guideline?[edit]

Hi, I'm wondering if the editors of this page consider this to be a full guideline. The tag at the top is different from more accepted guidelines, and that makes me wonder. One thing i'm proposing is that you use the Template:guideline, rather than the tag you have now. Please discuss it here (i'll be posting this message on other pages that have this same tag). Thanks! Fresheneesz 20:42, 9 September 2006 (UTC)


This page doesn't seem to be useful in defining what is Common knowledge, only what isn't. It's a page of negatives without serving the purpose of giving any positive examples of when you *need not* cite a reference. I find it unhelpful as you can tell. Wjhonson 20:28, 3 February 2007 (UTC)

proposed accepted common knowledge[edit]

As Wjhonson mentions, this is only a long list of "Don't"'s. I propose we list some "do"'s:

  • Simple geographic information (e.g. "The Rio Grande separates the United States from Mexico", or "Central Park is in New York City") should be passable as common knowledge requiring no citations
  • There are four seasons in a year, 365 days in year.
  • The periodic table and other well-known models in science.

--Loodog 05:13, 28 April 2007 (UTC)

Four seasons in a year? Even that is suspect. Some places have effectively no seasons -- where temperature and rainfall are comparatively even. But if one refers to mid-latitude and polar areas, such is generally true. The Rio Grande separates Texas from Mexico and nearly bisects New Mexico.

I'd add commonplace animal behavior and characteristics. Cliché knowledge is usually true if it isn't contested.

For example, on tigers:

Tigers have stripes;

Tigers are land creatures;

Tigers are generally solitary;

Tigers largely hunt, kill, and eat large herbivores;

Tigers do not eat inorganic substances (such as concrete blocks or sheet metal) or wood.

Tigers have large, sharp teeth and claws;

Tigers run fast and have great power;

Tigers look much like domestic cats.

Tigers are native to south, southeast, and east Asia.

But this is cliché knowledge in itself of little use. What is more significant?

That no two tigers have the same stripe pattern, and that tiger skins themselves are striped. Neither is so obvious, let alone common knowledge, but both would need citation from reliable sources.

If tigers are solitary, then why are they solitary in contrast to lions?

If tigers occasionally kill something other than large herbivores, then which ones and under what circumstances?

Sharp claws and teeth? How large, and how sharp? How much force is behind them? How does a tiger use them to catch, subdue, and eat prey, or defend itself from other predators (including other tigers?)

How powerful is a tiger?


Animal classifications are often suspect; they can change. In recent years, Linnaeus' classification of the domestic dog has gone in the view of many biologists from Canis familiaris to Canis lupus familiaris -- that the dog has gone from being a species in its own right to a subspecies of a wolf because (1) dogs and wolves interbreed, (2) the time in which dogs have split as a population from wolves is not enough to permit speciation. Likewise, some biologists claim that birds are in fact dinosaurs. We need to be careful about this. Dogs and wolves have been longer in genetic separation than were the races of Man -- and anyone who describes Caucasoid, Mongoloid, and Negroid peoples as different species violates scientific norms. Paul from Michigan (talk) 18:49, 6 July 2008 (UTC)

Common Knowledge for Popular Culture items[edit]

We are having trouble figuring out how Common Knowledge applies to popular culture when the item in question is widely known item. Specifically this is related to discussion on Talk:List_of_One_Piece_characters as to whether something like "Monkey D. Luffy is a character in the anime One Piece" given its high profile nature would be considered common enough knowledge and related to that, whether such things as his nature of being a rubber man, or Zoro's use of three swords, etc. would be. WP:fict does not really say much on something that is considered widely acceptable and easily verifiable to someone who could see an image of it on the original source or advertisement. This article doesn't really say how to treat such popular culture elements either.Jinnai (talk) 18:31, 12 November 2008 (UTC)

one does not need to rely on "common knowledge" for things like this. The work itself is an accepted source for uncontroversial statements. That he's a character in the anime is sourced by citing an place where he's a character. That he's a rubber man is sourced by citing a place where it's visually obvious. Good faith doubts about such things need further discussion, but not all evidence has to be in words. In my experience most such questions are not really good faith disputes, but attempts to destroy content. But if its necessary to find a quote for Zorro being a swordsman it can be done--but asking for one where there is no doubt about it is usually an instance of disruption. DGG (talk) 01:12, 22 November 2008 (UTC)

Citations needed for translations of everyday words in foreign languages?[edit]

Should citations be required for stating the meaning of a common word? There is a disagreement over this at Talk:List of Avatar: The Last Airbender characters#Fact tag necessary for common language knowledge?. Thanks, rʨanaɢ talk/contribs 04:01, 2 December 2009 (UTC)

If it's common knowledge, why is it in Wikipedia[edit]

It seems to me that if it truly is common knowledge, it doesn't need to be documented in Wikipedia. We don't need an article stating the sky is blue or that most people have five fingers on each hand. Sterling.M.Archer (talk) 21:58, 7 August 2011 (UTC)

we do need to refer to the fact in the context of articles. Can you imagine an article on "sky" that does not say what color it is? And the article on hand says we have four fingers -- and a thumb. The article on finger explains the discrepancy. DGG ( talk ) 23:52, 7 August 2011 (UTC)

A fun take on what "everyone knows"[edit]

XKCD "Ten Thousand" -- Donald Albury 10:18, 9 May 2012 (UTC)

I have recently undone a change to the article Fahrenheit - a section about a "rule of thumb" for conversion between degrees Fahrenheit and degrees Celsius was deleted on grounds that the source supplied was not a reliable source. On the other hand, any 16-year old who has passed a maths exam should should be able to verify the truth of the statement. If no citation was given, somebody would shout "WP:OR", so how do we prove that this is not original research, but something that is common knowledge, that is correct and has been doing the rounds for years. Martinvl (talk) 19:56, 30 June 2013 (UTC)

The "source" was a question to Yahoo answers. That is not a reliable source.
As for the rule of thumb in question - there is no evidence that it is commonly used. It is a fairly useless "rule of thumb" - it is so easy to do the correct calculation instead. The rule of thumb is within 4 C of the correct answer for the range of outside temperatures in Europe, but is rather less useful for cooking where it underestimates the temperature in Centigrade by about 10% for commonly used oven settings.--Toddy1 (talk) 21:10, 30 June 2013 (UTC)
Well now we have a huge bit on this "rule of thumb", far larger than the real calculation. So the article is giving undue weight to the unreliably sourced "rule of thumb".--Toddy1 (talk) 06:05, 1 July 2013 (UTC)
The Wikipedia core content policy has three items - WP:NPOV, WP:V and WP:OR. In the example in question, it is self-evident that WP:NPOV has been observed. Any reader with a modicum of mathematics can verify the algorithm, thereby satisfying WP:V. IMO, the most contentious point is WP:OR. The fact that the algorithm exists in a publication, however dubious, in which the editors have no role is proof that there is no original research. My understanding is that the need for reliable sources only arises when the three core policies cannot be demonstrated by other means. Martinvl (talk) 09:39, 1 July 2013 (UTC)
What has been expressed above, then, seems like a definie violation of WP:SYNTHESIS. It's not up to any reader with a modicum of mathematics to verify algorithms themself and thus WP:V has NOT been satisfied. Furthermore, per Wikipedia:Citing sources, reliable sources are needed as a default, not as an alternative when "other means" can't be demonstrated.
@User:Martinvl, the matter is very simple, keep the content and find an actual reliable source. A quick search on Google Books or Google Scholar would solve the issue. MezzoMezzo (talk) 08:24, 10 July 2013 (UTC)