The forms of the tuiseal ginideach are shown below.What follows is of necessity an adequate but crude simplification of a very complex topic.

Changes occur or not in the tuiseal ginideach (*) to the article, an t-alt, if present; (*) to the initial letter of the word; and (*) to the end of the word.

Changes to the article and the initial consonant of the word in the tuiseal ginideach depend on the rules for masculine and feminine in the tuiseal ginideach. Thus there are only two possibilities in each case. As you go down the list below you will see how the three variables, consonants; vowels, and s in masculine and feminine are treated. Watch out for the "DeNTaLS rule" however: Ní shéimhítear DTS tar éis DNTLS - - DTS are not aspirated after DNTLS.

(A word of reassurance to you, a léitheoir dhil - - dear reader, there are many, many rules and exceptions to rules associated with the tuiseal ginideach which are only guessed at by many good speakers of Irish. Many express subtle degrees of meaning and nuance. I would love to say "when in doubt leave it out" but modern Irish is not yet ready to abandon its love affair with the tuiseal ginideach. The rules of lenition, séimhiú, in the tuiseal ginideach are easily presented but again there are numerous factors to take into account to get the nuance right. Happily of the 1,300,000 people in Ireland who claim a knowledge of Irish most are like yourself a learner and like you will be loath to criticise small mistakes which may not be mistakes at all but an indication of things to come. Keep practising. Keep on reading. Listen as much as you can. Speak as often as you can. Taithí a níonn máistreacht.)

We have already looked at the basic form of the nouns in the tuiseal ainmneach
with and without the definite article an t-alt.
We have considered the occasions when the tuiseal ginideach should be used.

Now I would like to discuss how masculine or feminine affects the definite article and the initial letters of words in the tuiseal ginideach and how the final syllable of a word changes or not in each of the five declensions

Later on I will discuss the plurals of nouns
in the tuiseal ainmneach and tuiseal ginideach
with or without the definite article.

To begin I am choosing words which do not change their endings to show the changes to the initial consonants or vowels. First I show the indefinite noun without the article (guthán baile) and then with the definite article (lár na hoíche)

I anticipate an amount of controversy and criticism from my description of the tuiseal ginideach gan an t-alt - the genitive case without the definite article (indefinite nouns). My own rule - - from what source I do not know - - was

Unfortunately in preparing this page I read the relevant sections of the grammar books and I find there are many many variations in practice such as obair bhaile and deoch bhainne where there is seimhiú following the feminine nouns obair - - work and deoch - - a drink. Yet Ó Dónaill's dictionary gives iall madra even though iall is feminine. I am sure many readers of these pages will have strong views on this (minor) point and I look forward to their advice. For myself I am content, initially, to popularise a simplified knowledge of the language so that learners can get to speak and write it quickly. Those Irish speakers whom you associate with and the books and articles you read may clarify such minor difficulties as these for you. Meanwhile the above rules have stood me in good stead over a lifetime. Nevertheless in what follows I give the forms which are shown in Ó Dónaill. I take the Fourth Declension - - An Ceathrú Díoclaonadh first because it is the easiest. Taking a cynical view I would suspect some lazy speakers of Irish put all nouns in this Díoclaonadh and that if Irish survives another millenium this Ceathrú Díoclaonadh will be dominant.