The most frequent motive is the removal of some difficulty in the sense, expression or metre of the text, and especially obvious gaps or corruptions which the interpolator endeavours to fill or to heal.
The whole work was in the hands of the writer of the seventh book of the Apostolic Constitutions, who embodies almost every sentence of it, interspersing it with passages of Scripture, and modifying the precepts of the second part to suit a later (4th-century) stage of church development; this writer was also the interpolator of the Epistles of Ignatius, and belonged to the Syrian Church.
Interpolation is sometimes due to an inopportune use of knowledge, as when a quotation or a narrative is made to agree with what the interpolator has read elsewhere.
It was long ago noticed that PseudoClement bears a very close resemblance to Pseudo-Ignatius, the interpolator of the Ignatian Epistles in the longer Greek recension.
Hylen, De Tantalo (Upsala, 1896), who considers the story of the thirst of Tantalus in the underworld to be due to the Orphic interpolator in the Nhcvta of the Odyssey, and the Pandareus story to be an innovation of the Alexandrine poets.