It is customary to discuss Modern Irish in terms of three dialects: Munster (An Mhumhain), Connacht, and Donegal (Dun na nGall). Linguistically, the differences between the dialects conform to a broad (but not universal) principle that the Munster dialects are more conservative in morphology than Connacht and Ulster, but can be more innovative in phonology. A selection of features is considered here.
The position of the stress accent offers a useful range of comparative evidence. In Munster the stress is usually on the first syllable, as in capall /'kapoU, but in a disyllabic or trisyllabic word it is on the second syllable if that syllable is long, as in hradan /'bradfin/. When the stress is on the second syllable and it begins with /r l n/, the preceding vowel is often syncopated, as in craiste < carraiste. Elsewhere, the stress is invariably on the first syllable. The effect of the initial stress pattern seems to have been most strongly felt in the northern dialects where unstressed long vowels are shortened (e. g., hradan Ghradan/), though there is also a general tendency to shorten long vowels anyway (e. g., lan /lan/).
There is a general tendency for nominal morphology to become simpler as one moves farther north. For example, Munster still preserves relatively complex rules for the formation of the genitive singular: (a) broadening or palatalization of the final con-sonant—e. g., capaill, hrad, dothan, athar; (b) final consonant palatalized and - e added— e. g., hroige; (c) end consonant broadened and - a added—e. g., feola; (d) consonant added to vowel—e. g., ceartan, fiched; (e) -(e)ach added—e. g., catharach; (f) stressed vowel altered—e. g., lae; and (g) no change—e. g., ri, file, tine. In northern dialects, the distinction between cases both in the singular and in the plural is greatly in decline, even in the genitive. As in Middle Irish, the crucial distinction to be maintained is
Between singular and plural, and this has given rise to some very complex plural markers, especially in Connacht—for example, lucht ‘load’: pl. luicht, luchtannai, luchtail (-ail as a plural marker is unique to Connacht). Nevertheless, even in Munster, which tends to be more conservative, we find plural markers such as - acha, - anna, - i, - iocha.
The short plurals do, however, survive in some dialects as the number form after numerals—for example, ubh ‘egg’: se uibhe ‘six eggs’: uibheachai ‘eggs’.
In all dialects, it is usual for the original 3 sing. - idh to be replaced by - ann.
There are two main sources of Classical Modern Irish: the vast quantities of bardic poetry preserved in manuscripts from the 16th century onward and the tracts of the bardic schools that were devised as the guides to proper usage.
Evidence for the spoken dialects has been preserved on tape in recordings from the early part of the 20th century onward. This rich collection of material has been exploited in various ways, from the detailed discussion of a single dialect to a survey of features throughout all the dialects.