Eclipsis

Irish, like all modern Celtic languages, is characterized by its initial consonant mutations. These mutations affect the initial consonant of a word under specific morphological and syntactic conditions. The mutations are an important tool in understanding the relationship between two words and can differentiate various meanings.

Irish uses two mutations on consonants: lenition (Irish: séimhiú) and (urú). (The alternative names, aspiration for lenition and nasalisation for eclipsis, are also used, but those terms are a bit misleading.)

Originally these mutations were phonologically governed external sandhi effects: lenition was caused by a consonant between two vowels, and eclipsis by a sequence of nasal stop + obstruent, also at the beginning of a word.

There are also two mutations, t-prothesis and h-prothesis, found on vowel-initial words.

See Irish phonology for a discussion of the symbols used on this page.

Lenition is symbolized in the orthography by an h following the consonant in question.

The other consonants do not change under lenition.

The definite article triggers lenition of:

The possessive pronouns that trigger lenition are mo "my", do "your (sg.)", a "his"

These were originally preceded by the particle do and often still are in Munster.

Lenition is blocked in these constructions if two coronals are adjacent.

The singular form is used after numbers and is lenited in the following cases:

Constructions of adjective + noun are written as compounds.

In these constructions coronals are lenited even following other coronals.

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