Most English words ending in -us, particularly those derived from Latin, replace the -us suffix with -i to form plurals. This is irregular, however: some words that end in -us do not pluralize with -i. Sometimes this is because they are not Latin words, and sometimes due to habit (e.g. campus, plural campuses). Conversely, some non-Latin words ending in -us or Latin words that would not have pluralized with -i in Latin are given an -i ending in English.
In between these two extremes are words that, despite not supporting a Latin plural on etymological grounds, are nonetheless widely pluralized with -i and as such are not immediately heard as incorrect by a substantial number of native speakers (e.g. octopi as a plural for octopus). The question of whether or not these alternative plural forms can be considered incorrect or not touches on the on-going prescriptivism versus descriptivism debate in linguistics and language education.
English nouns are inflected for grammatical number, meaning that if they are of the countable type, they generally have different forms for singular and plural. This article discusses the variety of ways in which English plural nouns are formed from the corresponding singular forms, as well as various issues concerning the usage of singulars and plurals in English. For plurals of pronouns, see English personal pronouns.
Phonological transcriptions provided in this article are for Received Pronunciation and General American. For more information, see English phonology.
In linguistics, grammatical number is a grammatical category of nouns, pronouns, and adjective and verb agreement that expresses count distinctions (such as "one", "two", or "three or more"). In many languages including English, the number categories are singular and plural. Some languages also have a dual number or other arrangements.
The count distinctions typically, but not always, correspond to the actual count of the referents of the marked noun or pronoun.