Initial Mutations in Irish

The English word "an" is in origin a reduction of "one": "an apple" started out its linguistic life as "one apple". But as time went by, the -n at the end was dropped before consonants, and nowadays we say "a boy" and "a girl", not "an boy" and "an girl". The same sort of thing happened in Irish. The word i "in", for instance, used to end in an -n (just like the corresponding English word in, or the Latin one in, or the Greek one en, etc.). Thus:

i leabhar in a book

i n-áit in a place

When the following word begins with a vowel, like áit, the n reappears, just as in English "an apple". But the Irish situation is a little more complicated than the simple English contrast of a vs. an. The n reappears not just as n-, but also in various other forms depending on the beginning of the following word. It's as if in English we said "a lot" and "an apple", but also "a moy" instead of "a boy" and "a ngirl" instead of "a girl".

This particular kind of change at the beginning of words in Irish is called eclipsis, and it's explained more fully below. There are other ways that the beginnings of Irish words change; as a class they're called "initial mutations". Until you're used to them, they make looking words up in a dictionary quite a challenge, since it's the beginning of the word that's changing. But in spelling, we leave the original letter there, even though we don't pronounce it, so that it's easy to tell the basic form of the word. (The opposite applies in Welsh spelling, where the original letter is replaced: coch "red" becomes draig goch "a red dragon".)

Lenition

The most common initial mutation is lenition, which we explain more fully elsewhere. A small example will suffice here. The little word a can mean either "his" or "her". If we mean "his", we follow it with lenition. So:

Without Lenition = "her"		With Lenition = "his"
a croí	her heart	a chroí	his heart
a máthair	her mother	a mháthair	his mother
a buachaill	her boyfriend	a chailín	his girlfriend

Similarly, in certain compound prepositions, lenition is the difference between "him" and "her". If you don't include the lenition, you'll always be "for her" or "against her", but never "for him" or "against him":

Without Lenition = "her" With Lenition = "him"

ina cóir for her ina chóir for him

ina coinne against her ina choinne against him

There are lots of other places where lenition happens grammatically, which would be explained in any proper grammar of Irish.

Eclipsis

In the change of eclipsis mentioned above, several different things can happen to the beginnings of words.

1. Nothing at all happens to words beginning with certain sounds (h, l, m, n, r and s):

Letter Original With i "in"

h halla a hall i halla in a hall

l leabhar a book i leabhar in a book

m mias a dish i mias in a dish

n nead a nest i nead in a nest

r ráiteas a statement i ráiteas in a statement

s siopa a shop i siopa in a shop

2. A simple n- is prefixed to vowels:

Letter Original With i "in"

a áit a place i n-áit in a place

e Éire Ireland i nÉirinn in Ireland

i ithir tillage soil i n-ithir in tillage soil

o óstán a hotel i n-óstán in a hotel

u uacht a will i n-uacht in a will

3. For words beginning with unvoiced sounds (c, f, p and t), the initial sound is replaced with its voiced counterpart (g, v, b and d respectively):

Letter Original With i "in"

c cás trouble i gcás in difficulty

f feidhm function i bhfeidhm working

p pub a pub i bpub in a pub

t tráth time i dtráth in (good) time

4. For words already beginning with those voiced sounds (b, d and g), the initial sound is replaced with its nasal counterpart (m, n and ng respectively):

Letter Original With i "in"

b bosca a box i mbosca in a box

d dán fate i ndán fated, in store

g gort a field i ngort in a field

Notice throughout that the original initial letter is still written when a word undergoes eclipsis, even though it isn't pronounced. Thus i bpub is pronounced as if it were i bub; only the b- is pronounced, but the original p- is still written. In the case of a word that begins with f-, the f-sound is replaced with a v-sound, written bh-. The original f is still written, of course. So now you know that bhf- is pronounced like a v.

Other Mutations

There are a couple of other intial mutations as well, although they're not as common or as important as eclipsis and lenition.

One is called lomadh, or "baring". It's where we might expect a mutation, but in fact nothing happens, except that h is prefixed to vowels. You've actually already seen an example of lomadh: it follows a when it means "her", as shown in the example above for lenition. This is more plain with a word beginning with a vowel, like athair "father". The form a athair (technically with lenition) means "his father", but a hathair, with lomadh, means "her father".
There's another mutation whereby t- is prefixed to masculine nouns beginning with a vowel after the article: úll "an apple", but an t-úll "the apple". Historically this is a development of lenition, although you'd never be able to tell that from the modern language.
Lastly, there's a variant of lenition occurring only after -n to initial s-. In normal lenition, we expect the s-sound to be replaced with a h-sound, but in this variety, it's replaced with a t-sound instead: súil "an eye", but an tsúil "the eye". Historically this should only happen with the article an "the", but it's spreading out rapidly to every leniting word ending in -n. Thus properly we should say aon sagart "any priest", but in normal speech we tend to say aon tsagart instead.