Irregular plural nouns are nouns that do not become plural by adding -s or -es, as most nouns in the English language do. You’re probably familiar with many of these already. For example, the plural form of man is men, not mans. The plural form of woman is women, not womans. There are hundreds of irregular plural nouns, and in truth, you must memorize them through reading and speaking. There are, however, some common patterns to look out for.
The most common irregular plurals
Nounsending in -f and -fe
Tomake a plural of a word ending in -f, change the f to a vand add es. Similarly, if a word ends in -fe, change the fto a v and add an s. The result for both types is a plural thatends in -ves. This spelling arose because of the difficulty ofpronouncing f and s together in English (an attempt to do thiswill produce a v sound).
Butof course, there are exceptions. (Aren’t there always?) Some words ending in -othat are borrowed from other languages take only an s to make a plural,such as pianos, cantos, photos, and zeros. Cello, which isan abbreviation of the Italian word violoncello, can be written thetraditional way, celli, or the commonly accepted anglicized way, cellos.
Nouns that change vowels
ManyEnglish words become plural by changing their vowels, such as oo to eeor an to en.
Funfact: The eighteenth-century Americandictionary reformer Noah Webster preferred spellings that were closer to theirmost common pronunciations. Thus, he advocated for the return of the OldEnglish plural wimmen. Wouldn’t that have been convenient?
Irregular nouns that change substantially
Fora variety of historical reasons, some words change in spelling substantiallywhen made plural.
louselice
SingularPluralmousemicediediceoxoxenchildchildrenpersonpeople*pennypence(in British usage)
Irregular nouns that do not change at all when made plural
SomeEnglish nouns are identical in both the singular and the plural forms. Many ofthese are names for animals.
Singular/Plural (no change)sheepfishmooseswinebuffaloshrimptrout
Ihave seen several deer when walking in the woods near here.
Howmany shrimp did you catch?
Aircraft,watercraft, hovercraft, and spacecraftare all the same whether singular or plural.
NASAhas made several different types of spacecraft in their fifty-nine-yearhistory.
Plurals of Latin and Greek words
Thereare certain words we use on a regular basis, especially in mathematical andscientific contexts, that are borrowed from Latin or Greek. Many of these wordsretain their Latin or Greek plurals in math and science settings. Some of themalso have anglicized plural forms that have come into common use.
Nouns ending in -us
Tomake a word ending in -us plural, change -us to -i. Manyplurals of words ending in -us have anglicized versions, formed bysimply adding -es. The latter method sounds more natural in informalsettings. If there is an anglicized version that is well accepted, this will benoted in the dictionary entry for the word you are using.
Withthe double i, radii (pronounced RAY-dee-i) sounds unwieldy, butif you are a mathematician, you probably use it every day. If you are azoologist, you might say, “Hey, did you see those hippopotami?” but itwould sound silly on a casual visit to the zoo. Many people resist the spellingoctopuses, but it is perfectly acceptable. In fact, if you put a finepoint on it, since octopus is of Greek origin rather than from Latin,theoretically the spelling should be octopodes, not octopi.
Irregular formation of nouns ending in -is
Nounswith an -is ending can be made plural by changing -is to -es.Some people have a hard time remembering that the plural of crisis is crisesand the plural of axis is axes, but crisises and axisesare incorrect.
Singular(-is)Plural (-es)axisaxes (this is also the plural ofax and axe)analysisanalysescrisiscrisesthesistheses
Wordsending in -um shed their -um and replace it with -a toform a plural. The plurals of some of these words are far better known thantheir singular counterparts.
Nounsending in -ix are changed to -ices in formal settings, butsometimes -xes is perfectly acceptable.
Singular(-ex, -ix)Plural (-ces, -xes)indexindices(or indexes)appendixappendices (or appendixes, in a medical context)vortexvortices(or vortexes)
Theserules for irregular plural nouns must simply be memorized, although it ishelpful to understand the patterns first in order to master them. We also haveinformation on the Grammarly blog about patterns for regular nouns.
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