The declension of nouns is often a scary topic for native English speakers, but it doesn't have to be. Just because most of our nouns don't change (some still do!) it doesn't mean that we don't still have those grammatical parts in our sentences. Understanding these grammatical parts will be much more important — in some cases, absolutely essential — in other languages.
A noun case represents the grammatical role that a noun plays in a sentence. There are seven noun cases of which you should be aware: the nominative, the accusitive, the genitive, the prepositional (locative), the dative, the instrumental, and the vocative.
In Latin-based languages, understanding of these parts of speech is mostly only necessary for pronouns. However, Germanic languages decline nouns through several of these cases, and Slavic languages use them all! There may be many more cases (Finnish appears to have fifteen!) which are necessary in some other language I don't know about yet, but for now let's cover the seven basic cases.
To nominate is to name, and the nominative case names the noun. This is the default grammatical case for all nouns, and it is used to name the subject of a sentence. In the example:
The man has a cup of water.
The man is the subject, so it would be said to be in the nominative case.
The accusative case describes the noun which is the direct object. It is the noun upon which the verb is acted by the subject. In the example:
The man has a cup of water.
A cup is the noun being had by the man, so it would be said to be in the accusative case.
Latin root of the word dative means to give, and the dative case represents the recipient. It is the indirect object, or the recipient, of the action. In the example:
The man gave a cup of water to his friend.
His friend is the recipient of the verb to give, and would be said to be in the dative case.
The word genitive comes from the Greek word genesis, meaning the origin or the source. This case is used to indicate possession, measure, or origin of something else, usually another noun. It's easiest to think of it as the part that follows the word "of" or "from" in a phrase. In the example:
The man spilled a cup of water.
The water is the thing being measured, so it would be in the genitive case. To be clear, let's look at another. In the example:
A man from Italy spilled water.
Italy is the origin (of the man), and would be genitive.
The root position in the word prepositional gives away the fact that what's important here is location. No surprise that this is also sometimes known as the locative case. The prepositional case denotes a spatial or temporal relation or location. In the example:
A man in the hallway spilled his water.
The hallway is the location where the action occurred, and would be in the prepositional case.
An instument is something you use to perform some task, and a noun in the instrumental case is used to carry out the action in a sentence. In the example:
The janitor is cleaning the spilled water with his mop.
His mop is the instrument being used by the janitor to carry out the action, and would be said to be in the instrumental case.
Reflective its Latin root meaning "to call", the vocative is used for calling someone or something. It indicates a noun that is being addressed. In the example:
John, be careful on that wet floor.
John is being addressed and would be in the vocative case.
Noun declension (declining a noun through its cases) is mostly unused in the English language, except for personal pronouns and occasional (often ignored) grammatical constructs like choosing whether to use who or whom.
The personal pronoun I can only be used as the subject of a sentence, so it is nominative. The pronoun me, however, can be a direct object (accusative), an indirect object (dative), or as an instrument by adding "by" or "with". And in the genitive, we must use mine.
While this goes mostly unused in English, however, it will be necessary in many other languages. The endings of German nouns change as they are declined through the first four cases. Russian noun endings change for the first six. Ukrainian and Polish nouns go though all seven. And it looks like Turkish (a language in which I have future interest) uses additional, less common cases that aren't even on this list!
But even if you're learning a more noun-friendly language, as I am this year with Italian, there will still be some situations where understanding the grammatical roles noun play in a sentence will help you to choose the right one. We'll get to that soon...
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