Gweles an bennfenten rag A Guide to Irish Cases

==Intro==

Different languages have different strategies for showing the relationships between parts of a sentence. In English, we tend to use small, 'filler' words and word order as tools to show these relationships; for example, when we want to show the spacial relationship between two objects, we use prepositions like 'on', 'below' or 'beside' depending on what best suits the relationship. Or perhaps when we want to show how one object is related to another, we put the two words together, like in the phrase 'grammar guide', the first word is describing some aspect of the second one, in this case it's showing what kind of guide it is. However, in some languages there is an extra variable that helps to show listeners these relationships; grammatical case.

==What are Cases?==

Cases are different forms of the same basic word that emphasise different roles the word has in the sentence, ie. Whether it's acting or is being acted upon, whether it's being affected by a preposition, whether it's related to another noun or not, etc. These forms can be relatively minor changes (cúblálaí 'manipulator'; an cúblálaí, a chúblálaí, an chúblálaí) or they can be fairly different (bean 'woman'; an bhean, a bhean, na mná), what underpins them all is that there is some change to the noun between the different forms.

In Irish there are 3 cases that all have their own jobs and provide different pieces of information about the state the noun is in. These are the common case (an tuiseal ainmneach), the genitive (an tuiseal ginideach) and the vocative (an tuiseal gairmeach).

*Whether a noun is singular or plural does not affect what case it is in.

==The Nominative==

The nominative case (or tuiseal ainmneach 'subject case') is the form of the noun any learner regardless of grammar knowledge, conversational level or depth of study will be most familiar with. It is the basic, 'default' case used for simple sentences such as 'feiceann an madra an buachaill' (the dog sees the boy)  and it is the form that appears in the dictionary due to the fact that all other cases derive their form by changing from the nominative, minus some irregular words.

Nouns in the nominative (and in fact, in all cases) are split up into 3 groups based on gender; masculine nouns,feminine nouns and plural nouns. All singular nouns have 'an' as their article in the nominative, however, it's only feminine nouns that get a séimhiú (lenition/aspiration) after the article. Eg. An comhlacht 'the company' vs an bheocht 'the livliness'. Adjectives attached to feminine nouns also get a séimhiú, whereas ones attached to masculine nouns don't. Eg. Comhlacht mór 'a big company' vs beocht bhréagach 'false livliness'. 

In the case of nouns that start with vowels though things change a little bit. After 'an', masculine nouns starting in a vowel get a 't-' attached to their beginning (eg. An t-éan 'the bird', from éan 'a bird'). This doesn't happen to féminine nouns (eg. An aibítir 'the alphabet', from aibítir 'alphabet'). 

Lastly, plurals take the article 'na'. This article does not cause any changes (eg. Na fir 'the men'), unless the word starts with a vowel, in that case it adds a h to the start (eg. Athruithe 'changes', na hathruithe 'the changes'). Adjectives also gain an -a at the end if broad or an -e if slender (eg. Ainmhithe móra/fiáine 'big/wild changes'). 

To summarise:

===Masculine===

*Take 'an' without change (an comhlacht) 
*Adjectives don't change (comhlacht mór) 
*Nouns starting with vowels gain a t- at the start after 'an' (an t-éan, from éan)

===Feminine===

*Take 'an' with a séimhiú (an bheocht) 
*Adjectives get a séimhiú (beocht bhréagach) 
*Nouns starting with vowel get nothing after 'an' (an aibítir)

===Plural===

*Take 'na' with no change (na fir 'the men') 
*Broad adjectives get -a at the end (ainmhithe móra 'large animals) 
*Slender adjectives get -e at the end (ainmhithe fiáine 'wild animals') 
*Nouns starting with a vowel get h at the start after 'na' (na hathruithe 'the changes')

==The Genitive==