Declension


In linguistics, declension is the changing of the form of a word, generally to express its syntactic function in the sentence, by way of some inflection. The inflectional change of verbs is called conjugation.
Declensions may apply to nouns, pronouns, adjectives, adverbs, and articles to indicate number, case, gender, and a number of other grammatical categories.
Declension occurs in many of the world's languages. Declension is an important aspect of language families like American, Indo-European, Bantu, Semitic, Finno-Ugric, Turkic.
Old English was an inflectional language, but largely abandoned inflectional changes as it evolved into Modern English. Though traditionally classified as synthetic, Modern English has moved towards an analytic language.

History

It is agreed that Ancient Greeks had a "vague" idea of the forms of a noun in their language. A fragment of Anacreon seems to confirm this idea. Nevertheless, it cannot be concluded that the Ancient Greeks actually knew what the cases were. The Stoics developed many basic notions that today are the rudiments of linguistics. The idea of grammatical cases is also traced back to the Stoics, but it's still not completely clear what the Stoics exactly meant with their notion of cases.

Modern English

In Modern English, the system of declensions is so simple compared to some other languages that the term declension is rarely used. Most nouns in English have distinct singular and plural forms and have distinct plain and possessive forms. Plurality is most commonly shown by the affix -s, whereas possession is always shown by the clitic -'s attached to the noun. Consider, for example, the forms of the noun girl:
SingularPlural
Plaingirlgirls
Possessivegirl'sgirls'

Most speakers pronounce all of the forms other than the singular plain form exactly the same. By contrast, a few nouns are slightly more complex in their forms. For example:
SingularPlural
Plainmanmen
Possessiveman'smen's

In that example, all four forms are pronounced distinctly.
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:
SingularPlural
SubjectiveIwe
Objectivemeus
Dependent possessivemyour
Independent possessivemineours

Whereas nouns do not distinguish between the subjective and objective cases, some pronouns do; that is, they decline to reflect their relationship to a verb or preposition, or case. Consider the difference between he and him, as in "He saw it" and "It saw him"; similarly, consider who, which is subjective, and the objective whom.
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:
MasculineFeminineNeuter
Neuter
Subjectivehesheitthey
Objectivehimheritthem
Dependent possessivehisheritstheir
Independent possessivehishersitstheirs

The distinguishing of neuter for persons and non-persons is 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 or a hypothetical person where gender is insignificant. 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 and alumna. 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. 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 and blonde. 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 as it was declined in Old English.

Latin

Just as verbs in Latin are conjugated to indicate grammatical information, Latin nouns and adjectives that modify them are declined to signal their roles in sentences. There are five important cases for Latin nouns: nominative, genitive, dative, accusative, and ablative. Since the vocative case usually takes the same form as the nominative, it is seldom spelt out in grammar books. Yet another case, the locative, is limited to a small number of words.
The usual basic functions of these cases are as follows:
The genitive, dative, accusative, and ablative also have important functions to indicate the object of a preposition.
Given below is the declension paradigm of Latin puer ‘boy’ and puella ‘girl’:
CaseSingularPluralSingularPlural
Nominativepuerpuerīpuellapuellae
Genitivepuerīpuerōrumpuellaepuellārum
Dativepuerōpuerīspuellaepuellīs
Accusativepuerumpuerōspuellampuellās
Ablativepuerōpuerīspuellāpuellīs

From the provided examples we can see how cases work:
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.
Sanskrit grammatical cases have been analyzed extensively. The grammarian Pāṇini identified six semantic roles or karaka, which correspond closely to the eight cases:
For example, consider the following sentence:
Here leaf is the agent, tree is the source, and ground is the locus. The endings -aṁ, -at, -āu mark the cases associated with these meanings.

Declension in specific languages