Some nouns have identical singular and plural. Many of these are the names of animals:
The plural is sometimes formed by simply changing the vowel sound of the singular (these are sometimes called mutated plurals):
|mouse||mice (computer mouse can also take the regular plural form mouses)|
This group consists of words that historically belong to the Old English consonant declension. There are many compounds of man and woman that form their plurals in the same way: postmen, policewomen, etc.
The plural of mongoose is mongooses. Mongeese is a back-formation by mistaken analogy to goose / geese and is often used in a jocular context. The form meese is sometimes also used humorously as the plural of moose — normally moose or mooses — or even of mouse.
Irregular plurals from Latin and Greek
- Final a becomes -ae (also -æ), or just adds -s:
|encyclopaedia (or encyclopædia) / encyclopedia||encyclopaedias / encyclopedias (encyclopaediae and encyclopediae are rare)|
Scientific abbreviations for words of Latin origin ending in -a, such as SN for supernova, can form a plural by adding -e, as SNe for supernovae.
- Final ex or ix becomes -ices (pronounced /ᵻsiːz/), or just adds -es:
Some people treat process as if it belonged to this class, pronouncing processes /ˈprɒsᵻsiːz/ instead of standard /ˈprɒsɛsᵻz/. Since the word comes from Latin processus, whose plural in the fourth declension is processūs with a long u, this pronunciation is by analogy, not etymology.
- Final is becomes es (pronounced /iːz/):
(Some of these are Greek rather than Latin words, but the method of plural formation happens to be the same.)
Axes (/ˈæksiːz/), the plural of axis, is pronounced differently from axes (/ˈæksᵻz/), the plural of ax(e).
- Final ies remains unchanged:
Specie for a singular of species is considered nonstandard. It is standard meaning the form of money, where it derives from the Latin singular ablative in the phrase in specie.
- Final um becomes -a, or just adds -s:
|agendum (obsolete, not listed in most dictionaries)||agenda means a “list of items of business at a meeting” and has the plural agendas|
|datum||data (Now usually treated as a singular mass noun in both informal and educated usage, but usage in scientific publications shows a strong American/British divide. American usage generally prefers to treat data as a singular in all contexts, including in serious and academic publishing. British usage now widely accepts treating data as singular in standard English, including educated everyday usage at least in non-scientific use. British scientific publishing usually still prefers treating data as a plural. Some British university style guides recommend using data for both the singular and the plural use and some recommend treating it only as a singular in connection with computers.)
In engineering, drafting, surveying, and geodesy, and in weight and balance calculations for aircraft, a datum (plural datums or data) is a reference point, surface, or axis on an object or the Earth’s surface against which measurements are made.
|forum||fora/forums (fora is rare and might only be used to refer to more than one original Roman forum.)|
|medium||media (in communication systems and digital computers. This is now often treated as a singular mass noun); mediums (spiritualists, or items of medium size)|
|referendum||referendums is often taken to mean plebiscites, and referenda as the propositions voted on. It is often argued that referenda is incorrect because it is a Latin gerund, which did not have a plural form, while the “propositions voted on” is more like a gerundive, which could be pluralised.|
|spectrum||spectra (as in power spectrum in electrical engineering)|
- Final us becomes -i (second declension, [aɪ]) or -era or -ora (third declension), or just adds -es (especially for fourth declension words, where the Latin plural was similar to the singular):
|prospectus||prospectuses (plural prospectus is rare although correct in Latin)|
|campus||campuses (The Latinate plural form campi is sometimes used, particularly with respect to colleges or universities; however, it is sometimes frowned upon. By contrast, the common plural form campuses is universally accepted.)|
|succubus||succubi (The word omnibus is similar in form but is originally dative plural, so cannot be pluralised to *omnibi: see The Motor Bus.)|
|syllabus||syllabi/syllabuses (in fact the Latin plural is syllabūs)|
|virus||viruses ( see Plural form of words ending in -us#Virus )|
|cactus||cactuses/cacti (in Arizona many people avoid either choice with cactus as both singular and plural.)|
|octopus||octopuses (note: octopi also occurs, although it is strictly speaking unfounded, because it is not a Latin noun of the second declension, but rather a Latinized form of Greek ὀκτώ-πους, eight-foot. The theoretically correct form octopodes is rarely used.)|
|platypus||platypuses (same as octopus: platypi occurs but is etymologically incorrect, and platypodes, while technically correct, is even rarer than octopodes.)|
- Final us remains unchanged in the plural (fourth declension – the plural has a long ū to differentiate it from the singular short ǔ):
|meatus||meatus (but usually meatuses)|
|status||status (but usually statuses)|
Colloquial usages based in a humorous fashion on the second declension include Elvii (better Latin would be Elvēs or Elvidēs) to refer to multiple Elvis impersonators and Loti, used by petrolheads to refer to Lotus automobiles in the plural.
Some Greek plurals are preserved in English (cf. Plurals of words of Greek origin):
- Final on becomes -a:
- Final as in one case changes to -antes:
|Atlas||Atlantes (statues of the Titan); but|
|atlas||atlases (map collections)|
- Final ma in nouns of Greek origin can become -mata, although -s is usually also acceptable, and in many cases more common.
Irregular plurals from other languages
- Some nouns of French origin add an -x, which may be silent or pronounced /z/:
|beau||beaux or beaus|
|bureau||bureaux or bureaus|
|château||châteaux or châteaus|
|tableau||tableaux or tableaus|
- Italian nouns, notably technical terms in music and art, often retain the Italian plurals:
Foreign terms may take native plural forms, especially when the user is addressing an audience familiar with the language. In such cases, the conventionally formed English plural may sound awkward or be confusing.
- Nouns of Slavic origin add -a or -i according to native rules, or just -s:
|kniazhestvo||kniazhestva / kniazhestvos|
|kobzar||kobzari / kobzars|
|oblast||oblasti / oblasts|
- Nouns of Hebrew origin add -im or -ot (generally m/f) according to native rules, or just -s:
|cherub||cherubim / cherubs|
|seraph||seraphim / seraphs (The Hebrew singular is “saraph”. “Seraph” is a back-formation from “seraphim”. The form “seraphims” occurs in the King James Version.)|
|matzah||matzot / matzahs|
|kibbutz||kibbutzim / kibbutzes|
Ot is pronounced os (with unvoiced s) in the Ashkenazi dialect.
- Many nouns of Japanese origin have no plural form and do not change:
Other nouns such as kimonos, ninjas, futons, and tsunamis are more often seen with a regular English plural.
- In New Zealand English, nouns of Māori origin can either take an -s or have no separate plural form. Words more connected to Māori culture and used in that context tend to retain the same form, while names of flora and fauna may or may not take an -s, depending on context. Many regard omission as more correct:
Plurals of compound nouns
The majority of English compound nouns have one basic term, or head, with which they end. These are nouns and are pluralized in typical fashion:
|able seaman||able seamen|
|head banger||head bangers|
|yellow-dog contract||yellow-dog contracts|
Some compounds have one head with which they begin. These heads are also nouns and the head usually pluralizes, leaving the second, usually a post-positive adjective, term unchanged:
|attorney general||attorneys general|
|bill of attainder||bills of attainder|
|court martial||courts martial|
|director general||directors general|
|fee simple absolute||fees simple absolute|
|ship of the line||ships of the line|
|chief of staff||chiefs of staff|
|procurator fiscal (in Scotland)||procurators fiscal|
It is common in informal speech to pluralize the last word instead, like most English nouns, but in edited prose aimed at educated people, the forms given above are preferred.
If a compound can be thought to have two heads, both of them tend to be pluralized when the first head has an irregular plural form:
|woman doctor||women doctors (no longer in common use)|
Two-headed compounds in which the first head has a standard plural form, however, tend to pluralize only the final head:
In military usage, the term general, as part of an officer’s title, is etymologically an adjective, but it has been adopted as a noun and thus a head, so compound titles employing it are pluralized at the end:
|brigadier general||brigadier generals|
|major general||major generals|
For compounds of three or more words that have a head (or a term functioning as a head) with an irregular plural form, only that term is pluralized:
|woman of the street||women of the street|
For many other compounds of three or more words with a head at the front — especially in cases where the compound is ad hoc or the head is metaphorical — it is generally regarded as acceptable to pluralize either the first major term or the last (if open when singular, such compounds tend to take hyphens when plural in the latter case):
|ham on rye||hams on rye/ham-on-ryes|
With a few extended compounds, both terms may be pluralized—again, with an alternative (which may be more prevalent, e.g. heads of state):
|head of state||heads of states/heads of state|
|son of a bitch||sons of bitches/sons-of-a-bitch|
With extended compounds constructed around o, only the last term is pluralized (or left unchanged if it is already plural):
Plurals without singulars
Some nouns have no singular form. Such a noun is called a plurale tantum. Examples include cattle, thanks, clothes (originally a plural of cloth).
A particular set of nouns, describing things having two parts, comprises the major group of pluralia tantum in modern English:
- glasses (a pair of spectacles), pants, panties, pantyhose, pliers, scissors, shorts, suspenders, tongs (metalworking & cooking), trousers, etc.
These words are interchangeable with a pair of scissors, a pair of trousers, and so forth. In the American fashion industry it is common to refer to a single pair of pants as a pant —though this is a back-formation, the English word (deriving from the French pantalon) was originally singular. In the same field, one half of a pair of scissors separated from the other half is, rather illogically, referred to as a half-scissor. Tweezers used to be part of this group, but tweezer has come into common usage only since the second half of the 20th century.
There are also some plural nouns whose singular forms exist, though they are much more rarely encountered than the plurals:
Singulars without plurals
Mass nouns (or uncountable nouns) do not represent distinct objects, so the singular and plural semantics do not apply in the same way. Some examples:
- Abstract nouns
- deceit, information, cunning, and nouns derived from adjectives, such as honesty, wisdom, beauty, intelligence, poverty, stupidity, curiosity, and words ending with “ness”, such as goodness, freshness, laziness, and nouns which are homonyms of adjectives with a similar meaning, such as good, bad (can also use goodness and badness), hot, and cold.
- In the arts and sciences
- chemistry, geometry, surgery, the blues, jazz, rock and roll, impressionism, surrealism. This includes those that look plural but function as grammatically singular in English: mathematics (and in British English the shortened form ‘maths’), physics, mechanics, dynamics, statics, thermodynamics, aerodynamics, electronics, hydrodynamics, robotics, acoustics, optics, computer graphics, cryptography, ethics, linguistics, etc.; e.g., Mathematics is fun; Cryptography is the science of codes and ciphers; theromodynamics is the science of heat. Data often functions as a singular in terms such as ‘data collection’ or ‘data processing’.
- Chemical elements and other physical entities:
- aluminum (US) / aluminium (UK), copper, gold, oxygen, nitrogen, carbon, equipment, furniture, traffic, air and water