Irish/Reference/Grammatical Changes

Grammatical Changes
Irish is an inflected language. Words undergo pronunciation and spelling changes depending on the role they play in a sentence. Some of the most common changes are described below. Later in this Wikibook you will learn when to apply these changes.

Lenition
Lenition is a "softening" (a.k.a. "aspiration") of the consonant sound at the beginning of a word or syllable. It only happens to certain sounds: b, c, d, f, g, m, p, s, t; other letters are unaffected. There are two ways lenition is shown in writing: the old style (seanchló), in which a dot is placed over the consonant, and the new/modern style, where an h is added after the consonant. Some of the many cases in which lenition is used are:
 * on feminine nominative singular nouns after the article (ex. an fhírinne = the truth)
 * on masculine genitive singular nouns after the article (ex. an chroí = the heart)
 * on adjectives after a feminine nominative singular noun (ex. fírinne gheal = bright truth)
 * on adjectives after a masculine genitive singular noun (ex. an chroí dhubh = the black heart)
 * on adjectives after weak plural nouns which end in a slender consonant (ex. fir bheaga = small men but croíthe beaga = small hearts)
 * after mo or do (ex. mo shaol = my life)
 * after a when it means "his" (ex. a shaol = his life)
 * after the vocative particle a (ex. A Dhia! = God!)
 * in the second part of a compound word (ex. seanmháthair = grandmother, literally "old mother")

“DNTLS”
One exception to the normal lenition rules is the infamous "dentals-dots" rule: if there is a d, t, or s (the consonants in "dots") which would be lenited, but the letter before it is one of d, n, t, l, or s (the consonants in "dentals"), it is not lenited it after all. Example: an teanga = the language - it may be instinctive to write  'an theanga ' since a nominative feminine noun after the article is normally lenited, but the dentals-dots rule overrides that.

The word sa also triggers the dentals-dots rule, possibly because sa is a combination of the words ins + an, even though the terminal N is not spoken. Examples: sa saol, sa teach.

However, note that this rule does not apply to lenition of attributive adjectives. For example: grian the = hot sun.

Other exceptions
In a similar vein to the dentals-dots rule, the letters b and p are left unlenited following an m, as in um bosca. This is a much more obscure exception than dentals-dots, so you won't run into it very often.

Also, the letter s is not lenited when it is directly followed by one of c, p, t, m, or f, since there's no way (in Irish) that you could pronounce something like shf or shc. There are no counterexceptions to this exception, at least. For example, you write do stair = "your history" instead of "do shtair".

Eclipsis
Eclipsis is an "eclipsing" of the initial consonant sound of a word by another consonant sound. It only affects seven sounds: b, c, d, f, g, p, and t; essentially what happens is that you only pronounce the eclipsing consonant(s) - the eclipsed letter gets totally left out of the pronunciation (except for ng). However, when writing one of these things you write the eclipsing letter followed by the eclipsed letter. The rules for what happens to each go like this: These rules have to be memorized, but it really doesn't take long once you start using them.
 * b is eclipsed by m to become mb
 * c is eclipsed by g to become gc
 * d is eclipsed by n to become nd
 * f is eclipsed by bh to become bhf (two letters, but one sound)
 * g is eclipsed by n to become ng (note that this is pronounced not just as a straight n, but as the hybrid ng sound, much like an ng in English, or a 'ny' sound as in piñata)
 * p is eclipsed by b to become bp
 * t is eclipsed by d to become dt

Eclipsis is used in many cases (though not as many as lenition, by far), among which are these: Note the interesting capitalization in eclipsed expressions: when capitalizing an eclipsed word, the eclipsed letter is in uppercase, not the eclipsing letter (eg. as an bPoblacht from above, and also na bhFear = of the men). However, if writing in all capitals, you may either put the eclipsing letter in uppercase or leave it in lowercase. Both variants exist (ex. NA BHFEAR or NA bhFEAR).
 * on plural genitive nouns after the article (ex. na bpóg = of the kisses)
 * after any of the plural possessive pronouns, like "our", "your" (pl.), "their" (ex. ár ngrá = our love, bhur bpósadh = your wedding, a gcostas = their cost)
 * after some preposition+article combinations - you'll have to memorize which ones, but they can be learned with use (ex. ar an mbord = on the table, ón gcósta = from the coast, as an bPoblacht = out of the Republic)
 * after the preposition i (ex. i mbosca = in a box)

Palatalization
Palatalization (caolú), sometimes called "slenderizing", is a change made to the last group of vowels in a word which transforms the word from having a broad ending to a slender ending. Depalatalisation (leathnú) is the reverse change; it transforms a word from having a slender ending to a broad ending. These changes are used frequently in Irish, mostly for changing nouns between singular and plural, or for switching between the various cases (nominative, genitive, dative, vocative). Here are a few representative examples which show the kinds of vowel changes involved:

The usual rule for palatalization is to add an i after the last vowel, and the usual rule for depalatalization is to remove a trailing i. These usual cases are shown in the top row of the above table.

Initial h
In some cases, when a word ending in a vowel (such as the preposition "le" or the plural definite article "na") is followed by a word beginning with a vowel, an initial "h" is added to the second word to make pronunciation easier.

Example:

Tá an bhialann in aice le hóstán.

Initial ts
Under certain circumstances, feminine nouns beginning with "s" may be modified to "ts".

Contractions and compounds
Some Irish words are abbreviated, contracted, or compounded in specific ways. This is especially common when combining a preposition with a pronoun or article.

Contracting mo and do
The possessive pronouns mo (my) and do (your [sing.]) are commonly contracted before an initial vowel"

Prepositional Pronouns
When a preposition's object is a pronoun, Irish normally combines the two into a single prepositional pronoun.

Prepositions and Articles
In some cases, when a preposition's object starts with something other than a pronoun, especially a direct article (an or na), the preposition will form a compound similar to a prepositional pronoun.

Examples:
 * faoi + an = faoin
 * faoi + a [numerical particle] = faoina