The "Rationale" is one of those vestments that is both rare and yet comes up relatively frequently -- perhaps for reason of its visual prominence -- though usually attached to the question of, "what is it?" The Catholic Encyclopedia has this to say of it:
Rational, an episcopal humeral, a counterpart of the pallium, and like it worn over the chasuble. At the present time it is only used by the Bishops of Eichstätt, Paderborn, Toul, and Cracow. As worn by the Bishops of Eichstätt, Paderborn, and Toul, the rationale is in the form of a humeral collar, ornamented in the front and back with appendages.In short, the rationale was essentially a regionally particular vestment that seems to have appeared in the 10th century or so in the German Empire and also has some co-relation -- at least in its origins -- with the breastplate of the Jewish High Priest.
The forms of the rationale varied but generally had a pallium like appearance:
The following photos show the rationale as used by the Archbishop of Krakow.
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| Photo by Nicola de Grandi |
By contrast, here is the form of the rationale as worn in Eichstätt:
