Middle Irish: The Language Between Old Irish and Modern Gaelic

Middle Irish, spoken and written from roughly the tenth through twelfth centuries CE, represents a transitional stage of the Goidelic Celtic language between the more grammatically archaic Old Irish and the later Early Modern Irish that would eventually diverge into Modern Irish, Scottish Gaelic and Manx, and this transitional character means Middle Irish texts show considerable grammatical simplification and variation relative to the stricter classical Old Irish literary standard, reflecting ongoing language change during a genuinely transitional period rather than a single fixed register.

Middle Irish continued and expanded the substantial vernacular mythological and legendary literary tradition established in Old Irish, including further redactions and expansions of the Ulster Cycle material and the ongoing development of the Fenian Cycle, centered on the legendary warrior-poet Fionn mac Cumhaill and his band of warriors, the Fianna, a body of legendary material that would remain popular in Irish and Scottish Gaelic oral and literary tradition for many centuries after the Middle Irish period itself. Middle Irish law tracts and glossed legal commentary from this period also preserve valuable indirect evidence of earlier pre-Christian Irish social and religious custom, since medieval Irish law drew partly on inherited native tradition alongside the Christian and Latin legal influences the church introduced after Ireland's conversion.