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Dia daoibh!

Welcome to the Lenition thread! Here, I am going to explain one of Irish's initial mutations: lenition. The rules of lenition are tricky for some people, but luckily, they are logical!

This thread is an expansion of the tips and notes in the lenition skill. You will find more pronunciation guides and examples here than in the tips and notes :)

As with the Irish course itself, we are going to focus on the rules used in An Caighdeán. Some rules differ from dialect to dialect.

What is Lenition?

Lenition, or séimhiú as it is called in Irish, is an initial mutation that affects the spelling and pronunciation of words that begin with certain letters, in certain situations. The meaning of the word doesn't change. Lenition is a letter h placed after the first letter of a word in these situations.

What letters can be Lenited?

Not all letters can be lenited. Let's look at the ones that can undergo lenition:

As you can see, only the letters B, C, D, F, G, M, P, S and T can be lenited.

How to pronounce a lenited word

When a word is lenited, the pronunciation is changed quite a bit. Let's look at some examples:

(The funny looking symbols between slashes are from the International Phonetic Alphabet. I recommend reviewing these :) The words in brackets are English approximations. They're not perfect guides, but should give you a feel for how the words are pronounced)

  • peann /pʲaːn̪ˠ/ (pee-ow-n) pheann /fʲaːn̪ˠ/ (fee-ow-n) pen
  • teach /tʲax/ (tya-k) theach /hax/ (hya-k) house
  • ceann /caːn̪ˠ/ (kyown) cheann /çaːn̪ˠ/ (khyown) head
  • bean /bʲan̪ˠ/ (ban) bhean /vʲan̪ˠ/ (van) woman
  • droim /d̪ˠɾˠiːmʲ/ (drim) dhroim /ɣɾˠiːmʲ/ (grim) back
  • glúin/ɡɫ̪uːnʲ/ (gloon) ghlúin /ɣɫ̪uːnʲ/ (ghloon) knee
  • máthair /mˠaːhəɾʲ/ (maw-her) mháthair /waːhəɾʲ/ (waw-her) mother
  • súil /sˠuːlʲ/ (sool) shúil /huːlʲ/ (hool) eye
  • freagra /fʲɾʲaɡɾˠə/ (fra-gra) fhreagra /ɾʲaɡɾˠə/ (ra-gra) answer

When is Lenition used?

Lenition is used in 7 main situations. You will come across some other instances as you progress through your Irish studies.

1. Feminine Nouns

Feminine nouns are lenited after the definite article an in the nominative case.


  • mairteoil beef, an mhairteoil the beef
  • bean woman, an bhean the woman

An exception to this rule is that feminine nouns beginning with d or t are not lenited. Another exception is that nouns beginning with s becomes ts if the s precedes a vowel, l, n or r.


  • an deasc the desk
  • an traein the train
  • an tsubh the jam
  • an tsláinte the health
  • an tsnaidhm the knot
  • an tsráid the street
2. Feminine Adjectives

Singular feminine nouns cause lenition of the following adjective.


  • bean mhaith a good woman
3. Possessive Adjectives

Lenition is added after the following possessive adjectives (if possible):

  • mo (my) e.g. mo chara (my friend)
  • do (your (singular)) e.g. do mhadra (your dog)
  • a (his) e.g. a theach (his house)

Note: a when used as a possessive adjective can mean his, her or their. You will usually be able to tell from context which one it is, but you can also listen out for the initial mutation for a hint :)

4. Numbers

Lenition is added, when possible, after the numbers one to six.

  • aon chapall amháin (one horse)
  • dhá mhála (two bags)
  • trí bhuidéal (three bottles)
  • ceithre chat (four cats)
  • cúig phráta (five potatoes)
  • sé mhadra (six dogs)
5. Vocative Case

The vocative case is used when addressing someone directly. Lenition is used after the vocative particle a. (Note: Masculine nouns and names are slenderised (as well as lenited) after the vocative particle. See examples below)


  • Cá bhfuil tú, a chailín? Where are you, girl?
  • An bhfuil ocras ort, a Cháit? Are you hungry, Kate?
  • An bhfuil Gearmáinis agat, a Phóil? Can you speak German, Paul? (Notice the i added to Pól)
6. Prepositions

Lenition occurs after the prepositions ar on, de off/of, den off the/of the, do to/for, don to the/for the, faoi under/about, ó from, roimh before, mar as, sa/san in the, trí through and um around/about.


  • ar shráid (on a street)
  • an t-ochtú lá de Mhárta (the eight of March)
  • don bhuacaill (to the/for the boy)
  • faoi thalamh (underground)
  • ó Chorcaigh (from Cork)
  • sa pháirc (in the park)
  • san Fhionlainn (in Finland)
  • mar shampla (as an example/for example)
7. Other Words

Lenition is also used after the phrase nuair a when, the prefixes ró- too and an- very, and the word if (unless the next word is or deir).


  • nuair a bhrisim when I break
  • ró-mhór too big
  • an-mhaith very good
  • má dhúnann sé if it/he closes


This is a handy mnemonic to learn! It refers to the main exception to the rules of lenition. If a word starts with d, t or s (the consonants in the word dots) and would normally be lenited, but is preceded by a word that ends with d, n, t, l or s (the consonants in the word dentals), then lenition does not take place.


  • an-te (very hot)
  • den sráid (off the street)

Why is Lenition Used Anyway?

You may be thinking "Alex, I get all this, but why is it done in the first place?!".

Basically, lenition takes place to allow for the flow of speech. In Irish sentences, pauses are almost always avoided, so using lenition allows for the sentence to flow more easily. Try it for yourself! Read some of the above examples out loud. Try saying them with lenition and without lenition. You should hopefully see that the example with lenition flows better (i.e. you don't really have to take a brief pause in order to change the shape of your mouth to go from one letter to another. It's almost as though one letter glides to the next (nuair a bhrisim vs. nuair a brisim))

Congratulations! You've made it! That's a lot of information to take in, so don't worry if it doesn't all make sense to you right away or if it takes a while to remember all the rules. After some practice, it will eventually click.

Hopefully this post was helpful for you. Feel free to bookmark this page or print it off and keep it for revision purposes.

If you have any questions about lenition, here is the place to ask!

After studying this post, I recommend reviewing (or starting) the Lenition skill :)

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October 11, 2015


Go raibh maith agat, Alex.

Go raibh maith agat, Alex. Bhí mé dtrioblóid leis séimhiú.

Brilliant. Thanks.

I really looked at this lesson in the Irish notes and just gave up. WAY too many to remember....but as I am doing the lessons a few of them are getting through...but then there is THIS exception and THAT exception and this is done.....just because it is...I will love it when I can just know because it "sounds" better but I wonder if I can keep at it that many years, lol.

Go raibh maith agat. Initial mutations are probably the hardest and most interesting aspects of Gaelige to learn and to learn about.

Is maith liom an alt seo. GRMA!

Thanks! Really helpful!

In the Caighdeán, not all words beginning with s are lenited; those that begin with sc, sf, sm, sp, st, and sv are not lenited.

Also, the “DeNTalS-DoTS” exception doesn’t apply to the second of your seven main situations, e.g. caint shaibhir, where saibhir is still lenited despite caint ending with a t.

Just found this. Thanks!

I have a question - How ignorant does one look if one forgets this rule? Because I have a feeling that's going to happen to me. Quite a lot.

Don't worry. It will happen a lot, but later the correct version will just "sound" better. :)

Wow! You know a lot of languages? How long do you spend on language study each day?

Is it true that in learning Irish, the most difficult part is at the beginning? Say the equivalent of two semesters? I think this isn't true with learning all languages, though.

thank you, as clear as it can be given it is confusing!

Peitseoga vs. Pheitsoga vs. Peitseog vs pheitseog. Why and when do these lenitions occur? I'm confused.

If I’m not mistaken, I’m pretty sure Péitseoga and Phéitseoga are both plurals, whereas the ones without the a are singular. Pheitseoga and phéitseog are both lenited.

go raibh maith agat

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