"Twa" is the Scots form of "two," and it appears throughout the tradition in titles, refrains, and narrative — "Twa Corbies," "twa dogs," "twa hearts." Its brevity and distinctive vowel give it a folk quality, and it is particularly associated with the ballad tradition, where the pairing of two figures, two birds, or two fates is a fundamental structural principle. In lyrics "twa" often introduces the essential dyad of love — two people, two hearts — with a simplicity that is more affecting than any elaboration.

Twa is one of the small, ancient numerals — "ane, twa, three" — that form the spine of Scots counting and appear in poetry from the earliest times. Its appearance in titles and opening lines ("Twa Corbies," "John Anderson My Jo, my jo") signals the Scots lyric tradition immediately. The "twa" of Scottish poetry is often a pairing in tension: two lovers, two choices, two worlds. The "Twa Corbies" (two ravens) in the famous ballad exemplify the way this numeral structures the moral geometry of Scottish narrative: two figures, two perspectives, one dark conclusion. For students, "twa" is a word whose brevity belies its structural importance in Scots verse.