Perilous Seat
There is a dangerous myth surrounding the chair. Anyone that sits and does not rightfully belong in the chair will be maimed or killed. The person who does sit there must be chaste and a virgin of all sin. This is much like the sword in the stone or the shield at the chapel. Everything is especially designated for one knight. This one knight being Galahad.
Originally, this motif about the seat and the grail belonged to Perceval, but the Lancelot –Grail cycle transferred it to the new hero Galahad in 1230. Perceval occupies the seat at Arthur’s court at Carduel in the earlier de Boron Didot version. According to many scholars, the motif of the dangerous seat can be further traced to Welsh, Cornish, and Breton mythology, where the bulk of the Arthurian legend came from. According to this theory, the Perilous seat was a half-remembered version of a Celtic kingship ritual that has parallels in the Irish Lia Fail. Irish Lia Fail is a stone that represents the coronation of the high kings of Ireland. Therefore, the original history and significance of the Perilous chair showcase objects acting as place markers, vessels or symbols of importance.
The table of Joseph of Arimathea (the grail table), which is discussed in chapter 21 of the Quest for the Holy Grail, also has one vacant seat. This table represents spirituality while the round table represents fellowship of Knights.