Irish words often change their spelling and pronunciation at the very beginning of the word.

This unique grammar feature is known as initial mutation.

There are two main types of mutations in the Irish language.

These are called lenition (séimhiú) and eclipsis (urú).

Understanding these changes will instantly improve your reading and speaking skills.

I’ll show you exactly how and when to use them below.

What is lenition (séimhiú)?

Lenition literally means “softening”.

In Irish, this process is called a séimhiú.

You create a séimhiú by adding the letter ‘h’ immediately after the first consonant of a word.

This changes the sound of that original consonant.

Only nine consonants in Irish can take a séimhiú.

These letters are B, C, D, F, G, M, P, S, and T.

Letters like L, N, and R never change.

Common triggers for lenition

There are specific grammatical rules that tell us when to add a séimhiú.

One of the most common triggers is singular possessive adjectives.

The words for “my” (mo), “your” (do), and “his” (a) always cause lenition.

Feminine singular nouns also take a séimhiú after the word “an” (the).

Numbers from one to six also require you to lenite the following noun.

What is eclipsis (urú)?

Eclipsis literally means to cover up or overshadow.

In Irish, this mutation is known as an urú.

You create an urú by placing a new letter at the very start of the word.

You pronounce the new letter and completely ignore the original starting letter.

Only seven consonants in Irish can be eclipsed.

These letters are B, C, D, F, G, P, and T.

Notice how the new eclipsing letter is always lowercase, while the original letter becomes capitalized if it isn’t already.

Common triggers for eclipsis

Just like lenition, there are specific words that trigger an urú.

Plural possessive adjectives are a very common trigger.

The words for “our” (ár), “your” plural (bhur), and “their” (a) always cause eclipsis.

The preposition “i” (meaning “in”) is another everyday trigger for eclipsis.

Numbers from seven to ten also require an urú on the noun that follows.

Regional variations in mutations

The Irish language has three main dialects with slightly different mutation rules.

The most noticeable difference happens when a noun follows a preposition combined with the singular word for “the” (an).

In the Munster and Connacht dialects, you must use eclipsis in this situation.

In the Ulster dialect, you must use lenition instead.

Both of these variations are completely grammatically correct.

You should simply choose the dialect region you prefer and stick with it consistently.