Lenition

Complete guide to Irish lenition (An Séimhiú): learn which consonants lenite (b, c, d, f, g, m, p, s, t), grammatical triggers, and pronunciation rules.

Mutations Lenition SéImhiú Grammar Phonology Lenition In Irish Irish Lenition Rules An SéImhiú

Lenition, known in Irish as An Séimhiú, is a fundamental sound change that softens the initial consonant of a word. It is a core feature of Irish grammar that affects nouns, verbs, and adjectives in specific contexts. In writing, lenition is shown by adding an ‘h’ after the initial consonant.

For example, the word for “boat” is bád. When lenited, it becomes bhád.

bád - a boat
mo bhád - my boat

You will encounter lenition constantly, so understanding its rules is essential for speaking and reading Irish correctly.

Historical background

The underlying principle of lenition is spirantisation, where a plosive (a stop consonant like p, t, k) is replaced by a fricative (a sound made with friction, like f, th, ch) formed at the same place in the mouth.

Historically, the lenition of d and t produced dental fricatives (the “th” sounds in English that and thing). Over time, these sounds evolved into the sounds we hear today for dh and th.

Spelling and Pronunciation

Lenition is indicated by writing an h after the affected consonant. In older texts, you may see a dot (a ponc séimhithe or buailte) written over the consonant instead.

The following table shows which consonants can be lenited and how their pronunciation changes.

Consonant	Lenited	Broad Pronunciation	Slender Pronunciation
`b`	`bh`	[w], [v]	[v′]
`c`	`ch`	[x]	[x′]
`d`	`dh`	[ɣ]	[j]
`f`	`fh`	(silent)	(silent)
`g`	`gh`	[ɣ]	[j]
`m`	`mh`	[w], [v]	[v′]
`p`	`ph`	[f]	[f′]
`s`	`sh`	[h]	[h], [x′]
`t`	`th`	[h]	[h], [x′]

The consonants l, n, r, h, j, v, w, and z are not lenited in standard written Irish.

Pronunciation Notes

gh / dh: Broad gh and dh are pronounced as a voiced velar fricative [ɣ], a sound not found in English but similar to a soft ‘g’ in Spanish agua. Slender gh and dh are pronounced like the ‘y’ in “yes” [j].
bh / mh: These are generally pronounced as v. Broad bh and mh at the beginning of a word are often pronounced as w, while the v sound is more common in Munster. mh can also cause the surrounding vowels to become nasalised.
ch: Broad ch is like the ‘ch’ in Scottish loch [x]. Slender ch is like the ‘h’ in “hue” or the ‘ch’ in German ich [x′].
sh / th: Both are usually pronounced as h. However, when a slender sh or th comes before a long a, o, or u, it is often pronounced [x′] (like slender ch).
- a Sheáin - [ə x′aːnʲ] - O Seán!
- mo sheol - [mə x′oːl] - my sail
fh: The combination fh is completely silent. A word beginning with fh is treated as if it begins with a vowel.

Historical pronunciation of 'dh' and 'th'

Originally, dh was pronounced like the voiced ‘th’ [ð] in that, and th was pronounced like the voiceless ‘th’ [θ] in thing. These sounds are no longer used in modern Irish, having merged with the sounds of gh and h respectively.

When Lenition is Blocked

In certain situations, lenition is blocked even when the grammatical rule calls for it. This often happens when a word ends in a consonant that is formed in the same part of the mouth as the initial consonant of the following word. This phenomenon is sometimes known by the older term an cadad.

The rule is applied most strictly for the coronal consonants, often called the “dentals rule”.

Coronal Consonants: d, n, t, l, s

The consonants d, t, and s are not lenited if they follow a word ending in d, n, t, l, or s. This rule is very common because of the article an.

don doras - to the door (not *don dhoras)
an-te - very hot (not *an-the)

Labial Consonants: b, m, p

Lenition of b, m, and p is often blocked after words ending in -m.

um bosca - around a box

Velar Consonants: c, g

Lenition of c and g is blocked in surnames after Mhic and Nic, which would normally cause lenition.

Bríd Nic Cárthaigh - Bridget MacCarthy
teach Sheáin Mhic Gabhann - Seán MacGowan’s house

Special Cases and Exceptions

s- to ts-: After the article an, s- is not lenited. Instead, it changes to ts- if followed by a vowel, l, n, or r. This is a separate mutation known as the t-prefix.
Consonant Clusters: Initial clusters like sc-, sp-, st-, sm-, sf-, spl-, spr-, scl-, scr-, and str- are never lenited.
Silent fh-: Because fh is silent, a word beginning with fh- followed by a vowel is treated as a vowel-initial word.
- m’fhear céile - my husband (like m’athair)
- D’fhoghlaim mé Gaeilge. - I learned Irish. (The past tense particle do becomes d')
- D’fhreagair sé an cheist. - He answered the question.
gan + f: The preposition gan (without) never lenites a following f.
- gan fear - without a man
- gan fadhb - without a problem

Phonetic lenition of l, n, and r

Although l, n, and r are not lenited in writing, their pronunciation can change in spoken Irish depending on the dialect. The unlenited sounds are “tense” or “strong” ([ʟ], [ɴ], [r]), while the lenited versions are “lax” or “weak” ([l], [n], [ʀ]). This distinction is audible but not reflected in standard spelling.

an leabhar (the book) vs. mo leabhar (my book)

When to Use Lenition

Lenition is triggered by a wide range of grammatical particles, words, and contexts.

Nouns

After the vocative particle a.
- a Cháit! - Kate!
- a Sheáin! - John!
After the article an with feminine singular nouns in the nominative case (except d, t, s).
- an bhean - the woman
- an chathaoir - the chair
After the article an with masculine singular nouns in the genitive case (except d, t, s).
- hata an fhir - the man’s hat
After the possessive pronouns mo (my), do (your, sg.), and a (his).
- mo theach - my house
- do chara - your friend
- a mháthair - his mother
After many prepositions when not followed by the article, including ar, de, do, faoi, ó, mar, roimh, trí, thar.
- ar bhord - on a table
- ó Chorcaigh - from Cork
After the combined preposition-article forms don (to the) and den (from the).
- don fhear - to the man
After the number aon (one) and the personal number beirt (two people).
- aon bhád amháin - one boat
- beirt pháistí - two children
In the second part of many compound words.
- seanbhean - old woman (sean + bean)
- scian phóca - pocket knife (scian + póca)

Verbs

In the past tense (preterite), imperfect tense, and conditional mood. This is historically due to a particle do, which is now often omitted.
- Bhí sé anseo. - He was here.
- Cheannaigh mé é. - I bought it.
- D’ól sí an tae. - She drank the tea.
After the negative particle ní (is not, does not).
- Ní thuigim. - I don’t understand.
After past tense particles like ar, gur, nár, níor.
- Ar chuala tú? - Did you hear?
- Dúirt sé nár tháinig sé. - He said that he didn’t come.
After the direct relative particle a.
- an fear a cheannaigh an teach - the man who bought the house
After má (if).
- má thagann tú - if you come
Verbal nouns after the preposition a (to).
- ag iarraidh tú a phósadh - trying to marry you

Adjectives

When modifying a feminine singular noun.
- bean mhaith - a good woman
When modifying a masculine singular noun in the genitive case.
- praghas an chóta mhóir - the price of the big coat
When modifying a plural noun that ends in a slender consonant.
- fir mhóra - big men

Other Cases

After prefixes like an- (very), fíor- (true/very), and sean- (old).
- an-mhaith - very good
- fíordheacair - very difficult
After the past/conditional form of the copula, ba.
- Ba mhaith liom tae. - I would like tea.
In certain fixed words.
- dhá (two), bhur (your, pl.), cheana (already), choíche (never), chomh (as), chun (to).

A note on the term 'aspiration'

Lenition is sometimes incorrectly called “aspiration”. Aspiration is a much weaker phonetic change where a puff of air follows a consonant, as with the ‘p’ in the English word “pin”. In Irish lenition, the consonant itself fundamentally changes (e.g., p becomes f). Therefore, “lenition” (from Latin for “to weaken” or “to soften”) is the more accurate term.