Two forms are possible (i.) modus ponens (which establishes the consequent set down in the major premise): if A is B, it is C (or C is D); A is B; therefore A is C (or C is D), and (ii.) modus tollens (which disproves the antecedent): if A is B, it is C (or C is D); A is not C (or C is not D); therefore it is not B (or A is not B).
Tithe-payers could also file bills in equity to establish a modus against a tithe-owner.
Such rigidity of principle need not be extended to the affairs of everyday contact between the Vatican and the Italian authorities, with regard to which, indeed, a tacit modus vivendi was easily attainable.
The Senate refused to ratify it; but a protocol provided for a modus vivendi pending ratification, giving American fishing vessels similar advantages to those contemplated in the treaty; and on the whole Mr Chamberlain's mission to America was accepted as a successful one in maintaining satisfactory relations with the United States.
To avoid a crisis at the time when the young king was about to come of age, the government yielded; and on the 10th of May Sagasta announced that a modus vivendi with the Vatican had been established.
Bisrnarck hoped, indeed, putting all questions of principle aside, to establish a modus vivendi; but even this was difficult to attain.
This agreement, known as the Chamberlain-Bayard treaty, was rejected by the Senate, and as a consequence it became necessary to carry on the fisheries under a modus vivendi renewed annually.
But the ministry never had any real hold over the country or parliament, and the dissatisfaction caused by the modus vivendi with Spain, which would have wrought much injury to the Italian wine-growers, led to demonstrations and riots, and a hostile vote in the Chamber produced a cabinet crisis (December 17, 1905); Signor Fortis, however, reconstructed the ministry, inducing the marquis di San Giuliano to accept the portfolio of foreign affairs.
Sigwart does not indeed shrink from this and greater absurdities; he reduces the first figure to the modus ponens and the second to the modus tollens of the hypothetical syllogism, and then, finding no place for the third figure, denies that it can infer necessity; whereas it really infers the necessary consequence of particular conclusions.
A custom also sprang up, and was common at the time of the Commutation Acts, for a tithe-owner to accept a fixed sum of money or fixed quantity of the goods tithable in place of the actual tithes, known as a modus decimandi, whether in respect of a whole parish or only of particular lands within it; and this could be sued for in the ecclesiastical courts.