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, like Manx and colloquial Scottish Gaelic, uses two mutations on consonants: lenition ( ) and eclipsis ( ) (the alternative names, aspiration for lenition and nasalisation for eclipsis, are also used, but those terms are misleading). Originally these mutations were phonologically governed external sandhi effects: lenition was caused by a consonant being between two vowels, and eclipsis when a nasal preceded an obstruent, including 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. Summary table This table shows the orthographical and phonological effects of both lenition and eclipses. Environments of Lenition After proclitics After the definite article The definite article triggers lenition of: a feminine noun in the nominative singular "the woman" a masculine noun in the genitive singular "of the man" e.g. , the man's car (car of the man) a noun in the dative singular, when the article follows one of the prepositions "from", "to" or "in" + = : "to the man" + = : "from the woman" + = : "in the tree"; "in the autumn" and are never lenited after the article: "the drink", although is feminine nominative singular "of the house", although is masculine genitive singular Where an would be lenited after the article, it becomes (rather than ), written ts: "the eye" (fem. nom. sg.) "of the world" (masc. gen. sg.) After the vocative particle "Bríd!" "Seán!" "my friends!" After possessive pronouns The possessive pronouns that trigger lenition are "my", "your (sg.)", "his" "my son" "your house" "his pen" After certain prepositions "out of a tree" "under a tree" "as a person" "from Cork" "before morning" "through frost and snow" "at Easter" "both men and women" "on a table" After the preterite/conditional of the copula "He was a big person." "That was nice of you." After the preterite preverbal particles "He was not a teacher." "I didn't give" "Was he a priest?" "Did he come?" After certain preverbal particles "I don't understand" "if he comes" "the man who will give it to me" A