In general, Wikipedia articles have singular titles; for example, our article on the Canis familiaris species is at Dog, not Dogs. This rule exists to promote consistency in our article titles, and generally leads to slightly more concise titles as well.
Exceptions exist for two general types of articles.
Exceptions
There are two main types of exceptions to this rule:
Articles on groups or classes of specific things. Some examples:
Articles on groups of distinct entities that are nevertheless often considered together (preceded almost invariably by the word "the"), such as the Florida Keys, the Americas, or the Rivers of New Zealand.
Things like Maxwell's equations, Legendre polynomials, Chebyshev polynomials, [the] Cauchy–Riemann equations, etc. The topic is naturally the set or family of equations, although in some contexts they may be referred to in the singular. (That is, such a polynomial—for example—is of interest only because it is part of the polynomial sequence called the Chebyshev polynomials, and the sequence is thought of for most purposes as a unit.) Similarly, one is much more likely to mention Arabic numerals than a particular Arabic numeral.
Things like Skew coordinates. Although one may speak of the second skew coordinate of a point, the article is on the system of coordinates.
Articles that actually distinguish among multiple distinct instances of related items can be sensibly given a plural title when the alternative would be to create an inappropriately large number of short articles, one on each instance. The various Zeno's paradoxes, for instance, are incorporated into one article, with a correspondingly plural name.
Band names and the names of sports teams such as The Beatles or the Seattle Seahawks should be at their plural title.
Articles about measurement units, including compound units, should generally be singular (so "Foot per second" rather than "Feet per second"). For measurement units formed by combining an object or event with a unit ("Lines per inch" or "Flashes per minute"), the plural form may be acceptable if overwhelmingly favored in definitions of the unit by reliable sources.
With irregular plurals whose usage far exceeds the usage of the singular, the common and unastonishing plural titles Bacteria, Algae, and Data are preferred over Bacterium, Alga, and Datum (although some would argue that data is a mass noun and, as such, is already singular).
In rare circumstances, we ignore the rules here in order to make the encyclopedia better.
These rules apply only to articles. Categories are almost always given plural titles, and many templates are as well.
Sometimes, however, a plural form will establish a separate primary topic. Windows does not redirect to Window, but rather to Microsoft Windows; Snickers is about the chocolate bar, while Snicker redirects to Laughter. It may also be the case that a singular form (Axe) has a primary topic, while a plural form (Axes, which is the plural of both Axe and Axis) does not, or vice versa (Android is a disambiguation page, but Androids redirects to Android (robot)).
Discussion and consensus among editors, possibly through a requested move, determines if there is or is not a primary topic. For instance, discussion and consensus might determine that Cars should redirect to Car (as it currently does), redirect to Car (disambiguation), or host a topic such as Cars (film).
In making such a determination:
A plural form is treated like any other topic.
The relationship between a singular and its plural is important, but not the only consideration. Because readers and editors are used to seeing titles at the singular form, and can be expected to search for them/link to them in the singular form, the intentional use of a plural form by a reader or editor can be evidence that a separate primary topic exists at the plural form. At the same time, readers and editors are used to the fact that plural forms usually redirect to their equivalent singulars and thus are likely to expect to be redirected to a singular title when looking for something else.
Since normally users can be expected to search/link for/to topics using the singular form, searching/linking with a plural form is likely to be for a topic named with the plural form, when applicable. Example: Queens, the New York City borough, is the primary topic for the plural form of "queen". At the same time, since readers and editors expect plural redirects, Parachutes is a WP:PRIMARYREDIRECT to the device rather than being about the Coldplay album.
If the singular is not usually treated as a countable noun, that makes it far more likely that a split is the best decision. For example, time is a straightforward and obvious primary topic, but usually we don't treat "time" as something with a plural. Accordingly, times does not redirect to time, but rather to a different topic (in this case Time (disambiguation)).
A plural of a countable noun should never be treated as a partial title match when determining primary topic.
Encyclopedic uses are given more weight than dictionary uses, per WP:NOTADICTIONARY. This may mean that if there is not an article at the singular form, it is more likely that a plural form can establish a separate primary topic.
Just as with any other title, a plural base title can direct to an article (Snickers), or to a disambiguation page (Suns). A plural base title can also redirect to an article (Bookends redirects to Bookend; Faces redirects to Face).
If separate primary topics are determined, add a hatnote from the plural page to the singular form (or vice versa).
Sometimes, what appears to be a plural form may also be a separate word, which can influence the primary topic decision. (Walls can be the plural of "wall", but can also be a separate placename or surname.)
Sometimes, even when a singular might be ambiguous and lead to a disambiguation page, a plural might be (relatively) unambiguous and lead to a particular singular use; Oranges leads to Orange (fruit), not to the disambiguation page at Orange. This is primarily because only a noun can be pluralized, and the only other "orange" whose notability rivals that of the fruit is the color, and even though technically an interior designer could talk about choosing among several different oranges for the color of the curtains, usually only the fruit is pluralized in common usage. The reverse can also be true, and often is: Paper is a stable primary topic, but papers is highly ambiguous (since "paper" is typically an uncountable noun), and accordingly redirects to paper (disambiguation).
Using a plural as a separate primary topic is not specifically encouraged or discouraged; this page only describes the conditions where it is appropriate to do so.
All of these apply to the reverse situation as well (Scissor redirects to Scissors; Tropic redirects to Tropics).
