A noun class is part of a system of noun categorization that is found in synthetic language and polysynthetic language families. Languages with noun classes can have as few as two or more than 20 different classes. The more noun classes a language has, the higher the degree of inflection of the language. Distinctions between noun classes tend to be based on referent characteristics, morphological similarities and arbitrary reasons.
Native English speakers who have studied Spanish, French or German in school are familiar with the concept of grammatical gender. In Spanish, for example, all nouns fall into one of two groups: masculine nouns or feminine nouns. In the field of linguistics, it has not been fully agreed upon whether to separate grammatical gender from noun class. Some linguists use “gender” to refer to all noun classes, and other linguists consider gender to be one special subtype of noun class. Linguists in this second category tend to use the term "gender" only when describing nouns in languages that have two to four noun classes.
The class into which a particular noun falls will often line up with the referent, which is the thing that is referenced by the noun. For instance, the Spanish word for “man” is masculine, and the word for “woman” is feminine. With other nouns, the division is based more on morphological similarities than referent characteristics, such as how words ending in "–a" are more likely to be feminine and words ending in "–o" are more likely to be masculine in Spanish. Other words fall into one or the other noun class based only on convention.
In languages that have a noun class system, the system can have two to more than 20 noun classes. All nouns must belong to a class, and they usually can belong to only one. Other parts of the noun phrase or sentence, such as adjectives, articles and verbs, will show grammatical agreement with the noun based on its class. Using another Spanish example, the article “la” is used only with singular feminine nouns, and “el” is used only with singular masculine nouns. English is no longer viewed as employing noun class, but residual signs of noun classes from older forms of English exist in select pronouns as well as a few nouns that retain gender-based endings, such as "actor" and "actress" as well as "waiter" and "waitress."
Common noun class categories include masculine vs. feminine, animate vs. inanimate, human vs. non-human and rational vs. non-rational. Some examples of less common categories are shape and consistency, classes that often appear in Athabaskan languages such as Navajo. Many African languages have multiple noun classes that can be difficult for English speakers to grasp at first, and a few Australian Aboriginal languages even have separate noun classes for edible fruits and vegetables, hunting weapons and things that reflect light.