IMPROPERI. – This is the name given to a series of lamentations in which the Lord reproaches the Jewish people for the ingratitude they have shown for his benefits. The ideas expressed therein are undoubtedly inspired by Scripture, but the text seems to derive from the apocryphal Esd. 13–24. They are sung on Good Friday during the adoration of the Cross, and were added to it together with the Byzantine trisagion.
The menologion of the Greeks places their origin during the reign of Theodosius, at the suggestion of a boy during an earthquake; he is said to have invited the people to sing: «Sanctus Deus, Sanctus fortis, Sanctus et immortalis, miserere nobis», to which formula was later added: «Qui crucifixus es pro nobis miserere nobis», a formula especially dear to the Monophysites, since it could lead to a misunderstanding of the sufficiently affirmed Trinitarian meaning that Jesus had been crucified only according to his humanity. Gregory VII obtained from the Easterners that it be definitively omitted in order to avoid interpretative scandals (Lettere a Sinodo: I, VIII, ep. I: PL 137, 492). The origin thus given is, however, legendary. The oldest version of the I. is found in the Pontificale of Prudenzio di Troyes (d. 861). The texts, with their variants, were collected by E. Marrène (De antiquis Ecclesiae ritibus, IV, Antwerp 1764, col. 129 ff.; G. M. Tommasi, Opera, ed. A. Vezzosi, V, Rome 1752, p. 86; R. J. Hesbert for Benevento (Paleogr. musicale, 14 [1934]). It is now generally accepted that the I. were composed in the sixth century and came to the West from the Church of Jerusalem. In twelve propositions, God’s benefits are recalled: the trisagion in Greek follows the first three, and the «Popule Meus» the following ones; after the final repetition of the refrain, the antiphons for the adoration of the Cross follow.