Modus in ecclesiastical law, signifies an exemption from the payment of tithes, and is of two kinds: first, a partial exemption, when it is called a modus decimandi; secondly, a total exemption, when it is called a modus de non decimando. There is a third species of exemption, called a real composition, where an agreement is made between the owner of lands and the parson or vicar, with the consent of the patron and ordinary, that the lands specified shall be exempt from tithes on such considerations as are contained in the stipulation, such as land or other real recompense given in lieu and satisfaction of the tithes to be relinquished. The modus decimandi is that which is generally meant when the term modus is used. It is defined to be a custom of tithing in a particular manner, different from that which the general law prescribes; and the custom must have existed from time immemorial. The modes of tithing established by these customs are exceedingly various: sometimes it is a compensation in work and labor, as that the incumbent shall have only the twelfth cock of hay, and not the tenth, in consideration of the landowner making it for him; sometimes it is a less quantity of tithe in a more perfect, in lieu of a larger quantity in a crude and imperfect state, as a couple of fowls in lieu of tithe eggs; sometimes, and more frequently, it consists in a pecuniary compensation, as twopence an acre for the tithe of land.
The modus de non decimando is an absolute exemption from tithes. It exists in four cases:
1. The ruler may prescribe that he and his progenitors have never paid tithes for ancient crown lands, and this prescription will be good.
2. One Church officer does not pay tithes to another officer his superior, nor the superior to the inferior, according to the rule that ecclesia ecclesiae decimos solvere non debet.
3. An ecclesiastical person, as a bishop, may prescribe to be exempt from paying tithes on the ground that the lands belong to the bishopric, and that neither he nor his predecessors have ever paid them.
4. The abbeys and monasteries at the time of their dissolution were possessed of large estates of land, a great part of which was held tithe-free, either by prescription or by unity of possession, which was, in fact, no more than prescription, or by the pope's bull of exemption, or by a real composition. Thus in 'England, for example, the statute of 31 Henry VIII, c. 13, which dissolved the larger abbeys, enacted that all persons who should come to the possession of the lands of an abbey then dissolved should hold them tithe-free, in as ample a manner as the abbeys themselves had formerly hell them. The lands which belonged to the Order of the Knights of St. John of Jerusalem and to the Order of the Cistercians are within the protection of this statute; and those of them, consequently, which were tithe-free before they came into the hands of the king still continue tithe-free, in whosesoever hands they may now be. Some lands have been made tithe free by special legislative acts. See Blackstone, Comnmentaries, 2:28; Selden, History of Tithes, chapter 13; Burton, Conmpendium of the Law of Real Property, page 367 sq.