« MOTU PROPRIO ». — In general, this indicates a document relating to a concession made by a sovereign on his own initiative, whether real or fictitious, taking its name from the first words with which the text usually begins. This formula is adopted either to justify the extraordinary character of the concession or to produce certain legal effects in favor of the beneficiary.
In the Papal Chancery, it constitutes a particular type of document dating from as early as the 15th century and continuing to the present day: written on paper, it bears the pope’s name at the top, like the briefs, and begins with the words « M. p. »; the signature, in the pope’s own hand, was expressed by the formula « Placet m. p. », followed by the initial of his baptismal name (today the formula « Placet » is omitted and the name is that of his pontificate); it lacks a seal and other formalities.