A rationale is a liturgical vestment worn by clergy, in particular by Bishops, in the Roman Catholic Church which uses full vestments. It is humeral ornament, a counterpart to the Pallium, an is worn over the chasuble. It is a large clasp, made of precious metal and ornamented with diamonds, whose edges are adorned with small bells. The word is more commonly used to mean an explanation of the basis or fundamental reasons for something.