Old Irish  Old Irish ("Goídelc"; ; ; ), sometimes called Old Gaelic, is the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from 600 to 900. The primary contemporary texts are dated 700–850; by 900 the language had already transitioned into early Middle Irish. Some Old Irish texts date from the 10th century, although these are presumably copies of texts composed at an earlier time period. Old Irish is thus forebear to Modern Irish, Manx, and Scottish Gaelic. Old Irish is known for having a particularly complex system of morphology and especially of allomorphy (more or less unpredictable variations in stems and suffixes in differing circumstances) as well as a complex sound system involving grammatically significant consonant mutations to the initial consonant of a word. Apparently, neither characteristic was present in the preceding Primitive Irish period, though initial mutations likely existed in a non-grammaticalized form in the prehistoric era. Much of the complex allomorphy was subsequently lost, but the sound system has been maintained with little change in the modern languages. Contemporary Old Irish scholarship is still greatly influenced by the works of a small number of scholars active in the late 19th and early 20th centuries such as Rudolf Thurneysen (1857–1940) and Osborn Bergin (1873–1950). Notable characteristics of Old Irish compared with other old Indo-European languages, are:  Old Irish also preserves most aspects of the complicated Proto-Indo-European (PIE) system of morphology. Nouns and adjectives are declined in three genders (masculine, feminine, neuter); three numbers (singular, dual, plural); and five cases (nominative, vocative, accusative, dative and genitive). Most PIE noun stem classes are maintained ("o"-, "yo"-, "ā"-, "yā"-, "i"-, "u"-, "r"-, "n"-, "s"-, and consonant stems). Most of the complexities of PIE verbal conjugation are also maintained, and there are new complexities introduced by various sound changes (see below). Old Irish was the only member of the Goidelic/Gaelic branch of the Celtic languages, which is, in turn, a subfamily of the wider Indo-European language family that also includes the Slavonic, Italic/Romance, Indo-Aryan and Germanic subfamilies, along with several others.