To make a good and ſufficient modus, the following rules muſt be obſerved. 1. It muſt be certain and invariable[1], for payment of different ſums will prove it to be no modus, that is, no original real compoſition; becauſe that muſt have been one and the ſame, from it's firſt original to the preſent time. 2. The thing given, in lieu of tithes, muſt be beneficial to the parſon, and not for the emolument of third perſons only[2]: thus a modus, to repair the church in lieu of tithes, is not good, becauſe that is an advantage to the pariſh only; but to repair the chancel is a good modus, for that is an advantage to the parſon. 3. It muſt be ſomething different from the thing compounded for[3]: one load of hay, in lieu of all tithe hay, is no good modus: for no parſon would, bona fide, make a compoſition to receive leſs than his due in the ſame ſpecies of tithe; and therefore the law will not ſuppoſe it poſſible for ſuch compoſition to have exiſted. 4. One cannot be diſcharged from payment of one ſpecies of tithe, by paying a modus for another[4]. Thus a modus of 1d. for every milch cow will diſcharge the tithe of milch kine, but not of barren cattle: for tithe is, of common right, due for both; and therefore a modus for one ſhall never be a diſcharge for the other. 5. The recompenſe muſt be in it's nature as durable as the tithes diſcharged by it; that is, an inheritance certain[5]: and therefore a modus that every inhabitant of a houſe ſhall pay 4d. a year, in lieu of the owner's tithes, is no good modus; for poſſlibly the houſe may not be inhabited, and then the recompenſe will be loſt. 6. The modus muſt not be too large, which in law is called a rank modus: as if the real value of the tithes be 60𝑙. per annum, and a modus is ſuggeſted of 40𝑙. this modus will not be good; though one of 40s. might have been valid[6]. For, in theſe caſes of preſcriptive or cuſtomary modus's, the law ſuppoſes an original real compoſition to have been regularly made; which being loſt by length of time, the immemorial uſage is admitted
