From Barddas Vol II (my emphasis):
1. There are three Banded Bards.
The first is the Primitive Bard, or Poet, whose function and art are to poetize, and to preserve the memorial of every thing that is commendable in man or deed–to celebrate in song every thing that is commendable and good, as would be fitting in respect of what is meritorious and deserving–to teach in song every thing that is good in respect of doctrine and usages, and to maintain the memorial and teaching of the art of song, and all the privileges and usages which have been conferred upon the Bards of the Isle of Britain, and to teach them in methodical song, according to the proper art of vocal song of the Bards of the Ancient Cymry; And it is his duty to arrange and systematize matters, according to the privileges and usages of the Ancient Cymry, in every Chair and Eisteddvod, and Gorsedd of vocal song; it is incumbent upon him also to preserve and maintain the Cymric language free from degeneracy and corruption, and to teach it correctly, according to its quality and original and proper arrangement.
The second is the Herald-bard, whose office and art are memorial, instruction, and history–to symbolize good and laudable deeds, and to record in book and writing the genealogies and descent of the nation of the Cymry, their privileges and usages, so that they may be known, lest there should happen to the nation of the Cymry that degeneracy and ignobleness which impoverish the descent and privileges of a nation, and hence ensue non privilege and false privilege, and every lack of system, as has been the case with those unlearned nations, among which neither Awen from God, nor Bards, nor Bardism proceeding from that Awen, have been found. It is his duty to learn to read and to write the Cymric language, and to commit it to book and song properly and correctly, and to know the privileges and usages of the Bards of the nation of the Cymry, with their nature and essence. He ought also to impugn all ignobleness, all lack of privilege, all false privilege, and all illegality and disusage, lest the nation of the Cymry, their privileges and laudable usages, their language, innateness, and celebrated antiquity should suffer corruption.
The third is the Post-bard, whose art is vocal song according to the inventive instruction and skilful art of the later Bards, and to impart instruction in every science, wisdom, arts, and good and laudable usages, and to systematize new sciences according to kind, number, time, place, occasion, and dignity.
And this is the distinction between the Primitive Bard and the Post-bard: the Primitive Bard ought to bring with him what has been behind him from old ages, and the Post-bard ought to call to him what he sees before him; whilst the Herald-bard arranges these things according as the advantage, requirement, nature, essence, time, and dignity of them may demand; and to bestow instruction, sciences, wisdom, art, dignity, and honour out of them upon the nation and country of the Cymry, as befits what is good and praiseworthy.