Declension occurs in many of the world's languages. Among modern languages, declension is an important aspect of Arabic, Finnish, Turkish, Hungarian, many Amerindian languages such as Quechua, Bantu languages such as Zulu, Slavic languages such as Russian and Ukrainian, some Germanic languages such as High German, and some others. In the ancient world, languages that were highly declined included Sanskrit, Greek, Latin, and Hebrew. Old English was a moderately inflected language, as befits its Indo-European and especially its Germanic linguistic ancestry, but its declensions greatly simplified as it evolved into Modern English.
Declensions may apply to nouns, pronouns, adjectives, adverbs, numerals, and articles to indicate number (at least singular and plural), case (nominative or subjective, genitive or possessive, etc.), and/or gender. A declension is also a group of nouns that follow a particular pattern of inflection.
In the professional jargon specific to the language sciences, the term "declension" is sometimes used in a humorous way, to indicate where the meaning of an expression is off from the standard form; for example, comedy which is not funny could be said to have "humor declension".
In Modern English, the system of declensions is very simple compared to some other languages, so much so that the term declension is rarely applied to English in practice. Most nouns in English have distinct singular and plural forms and have distinct plain and possessive forms. Plurality is most commonly shown by the clitic -s (or -es), whereas possession is always shown by the clitic -'s (or by just the apostrophe for most plural forms ending in s) attached to the noun. Consider, for example, the forms of the noun girl:
Most speakers pronounce all of the forms other than the singular plain form (girl) exactly the same (though the elided possessive-indicating s of the plural possessive may be realised as [z] in some speakers' pronunciations, being separated from the plural-indicating s normally by a central vowel such as ). By contrast, a few nouns are slightly more complex in their forms. For example:
In that example, all four forms are pronounced in a distinct manner.
There can be other derivations from nouns that are not usually considered declensions. For example, the proper noun Britain has the associated descriptive adjective British and the demonym Briton. Though these words are clearly related and are generally considered cognates, they are not specifically treated as forms of the same word and thus not declensions.
Pronouns in English have even more complex declensions. For example:
Whereas nouns do not distinguish between the subjective (nominative) and objective (oblique) cases, some pronouns do; that is, they decline to reflect their relationship to a verb or preposition, or case. Consider the difference between he (subjective) and him (objective), as in "He saw it" and "It saw him"; similarly, consider who, which is subjective, and the objective whom (although it is increasingly common to use who for both).
The one situation where gender is still clearly part of the English language is in the pronouns for the third person singular. Consider the following:
The distinguishing of neuter for persons and non-persons is somewhat peculiar to English. This has existed since the 14th century. However, the use of the so-called singular they is often restricted to specific contexts, depending on the dialect or the speaker. It is most typically used to refer to a single person of unknown gender (e.g., "someone left their jacket behind"). Its use has expanded in recent years due to increasing social recognition of persons who do not identify themselves as male or female. Note that the singular they still uses plural verb forms, reflecting its origins.
For nouns, in general, gender is not declined in Modern English, or at best one could argue there are isolated situations certain nouns may be modified to reflect gender, though not in a systematic fashion. Loan words from other languages, particularly Latin and the Romance languages, often preserve their gender-specific forms in English, e.g. alumnus (masculine singular) and alumna (feminine singular). Similarly, names borrowed from other languages show comparable distinctions: Andrew and Andrea, Paul and Paula, etc. Additionally, suffixes such as -ess, -ette, and -er are sometimes applied to create overtly gendered versions of nouns, with marking for feminine being much more common than marking for masculine. Many nouns can actually function as members of two genders or even all three, and the gender classes of English nouns are usually determined by their agreement with pronouns, rather than marking on the nouns themselves.
Most adjectives are not declined. However, when used as nouns rather than adjectives, they do decline (e.g., "I'll take the reds", meaning "I'll take the red ones" or as shorthand for "I'll take the red wines"). Also, the demonstrative determiners this and that are declined for number, as these and those. Some adjectives borrowed from other languages are, or can be, declined for gender, at least in writing: blond (male) and blonde (female). Adjectives are not declined for case in Modern English, though they were in Old English. The article is never regarded as declined in Modern English, although formally, the words that and possibly she correspond to forms of the predecessor of the (s? m., þæt n., s?o f.) as it was declined in Old English.
Many European languages of Indo-European origin have a set of cases which are similar to those of Latin. For example German and other Germanic languages like Icelandic have similar cases but omit the vocative and ablative; classical Greek omitted the ablative and modern Greek also omits the dative; some Slavic languages also have the instrumental case.
Most of these languages have several declensions, i.e. classes of words with different schemes for determining the case endings. Furthermore, it is notable that in all these languages and declensions it is the exception rather than the rule for there to be a one-to-one correspondence between cases and endings, so that often one has to deduce from the context which case is meant.
Sanskrit, another Indo-European language, has eight cases: nominative, vocative, accusative, genitive, dative, ablative, locative and instrumental. Some do not count vocative as a separate case, despite it having a distinctive ending in the singular, but consider it as a different use of the nominative.
For example, consider the following sentence:
|from the tree||a leaf||to the ground||falls|
Here leaf is the agent, tree is the source, and ground is the locus. The endings -a?, -at, -?u mark the cases associated with these meanings.