If the Triad stood alone, the idea that it owes its origin to the effect of the doctrine of the Trinity upon the Celtic imagination might reasonably be entertained. The fact that this doctrine has led to many peculiar phenomena in Irish folklore, literature, and art has frequently been pointed out. Nor would I deny that the sacred character of the number three, together with the greater facility of composition, may have contributed to the popularity of the Triad, which is certainly the most common among the various numerical sayings as well as the only one that has survived to the present day.
However that may be, I believe that the model upon which the Irish triads, tetrads, pentads, &c., were formed is to be sought in those enumerative sayings—Zahlensprüche, as the German technical term is—of Hebrew poetry to be found in several books of the Old Testament. I am indebted to my friend the Rev. Carl Grüneisen for the following list of such sayings, which I quote in the Vulgate version.
Duads and Triads.
Ecclus. 23: 21, Duo genera abundant in peccatis, et tertium adducit iram et perditionem, &c.
Ib. 26: 25, In duobus contristatum est cor meum, et in tertio iracundia mihi advenit: 26 vir bellator deficiens per inopiam, et vir sensatus contemptus, 27 et qui transgreditur a iustitia ad peccatum, Deus paravit eum ad romphaeam.
Ib. 26: 28, Duae species difficiles et periculosae mihi apparuerunt: difficile exuitur negotians a neglegentia, et non iustificabitur caupo a peccatis labiorum.
Triads and Tetrads.
Proverb. 30: 15, Tria sunt insaturabilia, et quartum quod nunquam dicit: sufficit. 16 Inferuns, et os vulvae, et terra quae non satiatur aqua; ignis vero nunquam dicit: sufficit.
Ib. 30: 18, Tria sunt difficilia mihi, et quartum penitus ignoro: 19 viam aquilae in caelo, viam colubri super petram, viam navis in medio mari, et viam viri in adolescentia.
Ib. 30: 21, Per tria movetur terra, et quartum non potest sustinere: 22 per servum cum regnaverit: per stultum cum saturatus fuerit cibo, 23 per odiosam mulierem cum in matrimonio fuerit assumpta, et per ancillam cum fuerit heres dominae suae.