The eretide is everything that has happened in times foregone, as well as why it happened. It is the tale of the world, and all the folk in it and their deeds. As a field of knowhood, the eretide is learnt for what it can tell us anent today: how the world we live in was shaped by things foregone.
Western understanding of the eretide was for a long time shaped by the Bible, which was taken to be true to word, and by the writings of Greeks and Romans, which were the only witnesses to their time. Today's understanding of the eretide was built slow, first by putting together the sundry writings that were bequeathed and the leftovers that could be seen above ground.
Soon it was known that many more leftovers were hidden underground, and, what was more, they had lain unshifted for hundreds or thousands of years. By unearthing these leftovers our knowhood of times foregone could grow great. This was the birth of erelore, which has fedback into our knowhood of the eretide.
Even though the knowledge of the eretide has grown greatly since earlier times, there is yet a great fight between gainstanding understandings of the eretide. Each eretideman has their own thoughts on how to understand what has foregone, and this understanding is shaped by the way they see the world today. For, if one sees the world becoming more sinful and wrong, then they will see the eretide as a long slide from sinlessness to the sins of today.
Likewise, those who follow the teachings of Karl Marx see today's world as a fight between owners and workers, and would look into the eretide to see how the owners came to own, and the workers to work. Thus two eretidemen, who may both be well-learned and earnest, would make and build gainstanding eretides.