(Latin: casus, case)
The method followed by moral theologians of explaining moral principles through the presentation and solution of concrete cases. The principles may be ever so clear and evident; still it is not always easy to arrive at the correct solution in a given case.
For example, moral theology teaches that a person should be just in all his dealings. Now suppose that A enters into a contract to do some special work for B for which he is to receive a definite sum in fixed installments. Later A hears that B is not entirely reliable. May A quit the work or should he wait until the work is done, and then perhaps sue B?
Again, sometimes there is a conflict of duties. For example, the law of the Church obliges us to hear Mass on Sundays; the natural law demands that we help our neighbor who is in need. Suppose then that a person is sick and requires care. Should one stay with the sick person and miss Mass; or leave the person alone and go to church? Another example may be taken from the administration of the sacraments. The minister of the sacrament in Baptism must use the proper water and pronounce the correct form. Suppose he should use some water, which is not exactly prescribed, but which belongs to the species of water; or suppose that he should substitute one or two words for those which are required by the ritual; will the Sacrament thereby be invalid?
These examples illustrate the cases proposed and solved by moralists. Each individual case has its own proper features. Now it is certainly a great help to the confessor who has to give decisions in particular instances to know of analogous cases which have already been discussed and decided by moralists. He may then use such decisions as a basis for his own cases. Judges and attorneys follow the same procedure. The decisions rendered by the courts form precedents for the solution of similar cases. Though writers on moral subjects have from the beginning of the Christian era discussed practical questions, it is only within recent centuries that moral principles have been systematically discussed through the medium of concrete cases. Saint Alphonsus became the pioneer in the case method by adopting the "Medulla" of Herman Busembaum, which is largely casuistic, as the substratum of his own work in moral theology. Others have followed his example. At present a book treating on moral questions will not be considered up to date unless it contains the discussion of particular cases. The case material, it is true, should not occupy the entire space. The principles should be stated first, and followed by their appropriate case illustrations. Special cases, of course, are not to be decided by sentiment or what is popularly called common sense, but according to the principles under which they happen to fall. Cases of conscience are one of the exercises at the conferences of priests meeting usually about the ember-days four times a year.