It is unusual in that the movements vary greatly in style, and each uses a paraphrase technique for the original Sarum chant.
The circumstances of its composition are unclear; it may have been composed for the funeral of Charles VII in 1461; an alternative hypothesis is that it was written after the death of Louis XI in 1483.
It calls for four voices, and is in five parts: Since it lacks a Sanctus, Communion or Agnus Dei, most scholars consider it incomplete.
Since the document seems to have been intended as a complete collection of Ockeghem's music,[3] these movements were probably left out because they were either unavailable either to the copyist or not in a legible condition.
Richard Wexler proposed 1461, the year of Charles VII's death, a monarch to whom Ockeghem owed a debt of gratitude and for whom he would likely have composed a requiem.