All the Indo-European languages are more or less related to one another. We Irish must acknowledge a relationship, or rather a very distant connecting tie, with English. But, to trace this home, Irish must be followed back to the very oldest form of its words, and English must be followed back to Anglo-Saxon and when possible to Gothic. The hard mutes (p, t, c) of Celtic (and, for that matter, of Sanscrit, Zend, Greek, Latin, Slavonic, and Lithuanian) will be represented in Gothic by the corresponding soft mutes (b, d, g), and the soft mutes in Celtic by the corresponding, hard mutes in Gothic. Thus we find the Irish dia (god) in the Anglo-Saxon tiw, the god of war, whose name is perpetuated for all time in Tiwes-däg, now "Tuesday", and we find the Irish déad in the Anglo-Saxon "toth", now "tooth", and so on. But of all the Indo-European languages Old Irish possesses by far the nearest affinity to Latin, and this is shown in a great many ways, not in the vocabulary merely, but in the grammar, which for philologists is of far more importance,—as, for example, the b-future, the passive in-r, the genitive singular and nominative plural of "o stems", etc. Thus the Old Irish for "man", nom. fer, gen. fir, dat. fiur, acc. fer n—, plur. nom. fir, gen. fer n—, is derived from the older forms viros, viri, viro, viron, nom. plur. viri, gen. plur. viron, which everyone who knows Latin can see at a glance correspond very closely to the Latin inflections, vir, viri, viro, virum, nom. plur. viri, etc.
So much for the language. When did this language begin to be used in literature? This question depends upon another—When did the Irish begin to have a knowledge of letters; when did they begin to commit their literature to writing; and whence did they borrow their knowledge of this art?
The oldest alphabet used in Ireland of which remains exist appears to have been the Ogam, which is found in numbers of stone inscriptions dating from about the third century of our era on. About 300 such inscriptions have already been found, most of them in the southwest of Ireland, but some also in Scotland and Wales, and even in Devon and Cornwall. Wherever the Irish Gael planted a colony, he seems to have brought his Ogam writing with him.
The Irishman who first invented the Ogam character was probably a pagan who obtained a knowledge of Roman letters. He brought back to Ireland his invention, or, as is most likely, invented it on Irish soil. Indeed, the fact that no certain trace of Ogam writing has been found upon the European continent indicates that the alphabet was invented in Ireland itself. An inscription at Killeen Cormac, Co. Kildare, survives which seems to show that the Roman alphabet was known in Ireland in pagan times. Ogam is an alphabet suitable enough for chiselling upon stones, but too cumbrous for the purposes of literature. For this the Roman alphabet must have been used. The Ogam script consists of a number of short lines straight or slanting, and drawn either below, above, or through one long stem-line. This stem-line is generally the sharp angle between two faces or sides of a long upright rectangular stone. Thus four cuts to the right of the long line stand for S; to the left of it they mean C; passing through it, half on one side and half on the other, they mean Z. The device was rude, but it was applied with considerable skill, and it was undoubtedly framed with much ingenuity. The vowels occurring most often are also the easiest to cut, being scarcely more than notches on the edge of the stone. The inscription generally contains the name of the dead warrior over whom the memorial was raised; it usually begins on the left corner of the stone facing the reader and is to be read upwards, and it is often continued down on the right hand angular line as well.
The language of the Ogam inscriptions is very ancient and nearly the same forms occur as in what we know of Old Gaulish. The language, in fact, seems to have been an antique survival even when it was first engraved, in the third or fourth century. The word-forms are probably far older than those used in the spoken language of the time. This is a very important conclusion, and it must have a far-reaching bearing upon the history of the earliest epic literature. Because if forms of language much more ancient than any that were then current were employed on pillar-stones in the third or fourth century, it follows that this obsolescent language must have survived either in a written or a regularly recited form. This immediately raises the probability that the substance of Irish epic literature (which was written down on parchment in the sixth or seventh century) really dates from a period much more remote, and that all that is purely pagan in it was preserved for us in the same antique language as the Ogam inscriptions before it was translated into what we now call "Old Irish."
The following is the Ogam alphabet as preserved on some 300 ancient pillars and stones, in the probably ninth-century treatise in the Book of Ballymote, and elsewhere:
There are a great many allusions to this Ogam writing in the ancient epics, especially in those that are purely pagan in form and conception, and there can be no doubt that the knowledge of letters must have reached Ireland before the island became Christianized. With the introduction of Christianity and of Roman letters, the old Ogam inscriptions, which were no doubt looked upon as flavoring of paganism, quickly fell into disuse and disappeared, but some inscriptions at least are as late as the year 600 or even 800. In the thoroughly pagan poem, The Voyage of Bran, which such authorities as Zimmer and Kuno Meyer both consider to have been committed to parchment in the seventh century, we find it stated that Bran wrote the fifty or sixty quatrains of the poem in Ogam. Cuchulainn constantly used Ogam writing, which he cut upon wands and trees and standing stones for Queen Medb's army to read, and these were always brought to his friend Fergus to decipher. Cormac, king of Cashel, in his glossary tells us that the pagan Irish used to inscribe the wand they kept for measuring corpses and graves with Ogam characters, and that it was a source of horror to anyone even to take it in his hand. St. Patrick in his Confession, the authenticity of which no one doubts, describes how he dreamt that a man from Ireland came to him with innumerable letters.
In Irish legend Ogma, one of the Tuatha De Danann who was skilled in dialects and poetry, seems to be credited with the invention of the Ogam alphabet, and he probably was the equivalent of the Gaulish god Ogmios, the god of eloquence, so interestingly described by Lucian.
We may take it then that the Irish pagans knew sufficient letters to hand down to Irish Christians the substance of their pagan epics, sagas, and poems. We may take it for granted also that the greater Irish epics (purely pagan in character, utterly untouched in substance by that Christianity which so early conquered the country) really represent the thoughts, manners, feelings, and customs of pagan Ireland.