RATIONAL (SACRED SCRIPTURE). - Name given by the Vulgate (rationale) to the most sacred part of the ornament of the Jewish high priest, which he wore on his breast (hence also called the "pectoral" περατήθων by the Septuagint in Ex. 28:4) when he entered the sanctuary. In Ex. 28:15-30 there is a detailed description (cf. Sir. 45:10-11), which emphasizes its symbolic meaning.
It consisted of a quadrangular piece of cloth folded into a pouch (a kind of bag) of rich fabric woven of four colors and gold threads, like the ephod (v.), to whose upper clasps it was joined by means of gold chains and fastened to the belt with two cords of hyacinth. On it were set, in four rows of three, twelve precious stones all different, with the names of the twelve tribes of Israel engraved in gold. In this way the high priest, in the most solemn act of his functions, carried "the names of the children of Israel over his heart... for a continual remembrance before Jahweh" (Ex. 28:29). But the greatest prerogative of the rational was to contain the 'urim and tummim (v.), "light and perfection," from which the high priest drew the answers of Jahweh in important circumstances. Because of this purpose it is called in the Hebrew original hōshen hammishpat (or simply hōshen, of uncertain etymology, perhaps equivalent to "bag" or "ornament"), that is, "bag of the divine decisions" (λογεῖον τῶν κρίσεων "oracle of judgments"; Vulgate rationale indicii; Symmachus δόγιον "bag"; Flavius Josephus and other Greek versions simply λόγιον "oracle").
It seems that the rational is of Egyptian origin: in fact various personages of ancient Egypt have a kind of ornament in the shape of a trapezoid or square hanging from the neck over the breast (notable is the one found on the mummy of Queen A'āh-hotep, mother of Amosis I, founder of the XVIII dynasty, 1580-1558 B.C.: it is in the shape of a small temple finely worked with symbols and figures and precious stones set in mosaic).