A general rule intended to provide indirect or reflex certainty about the morality of a contemplated course of conduct when sufficient direct certainty cannot be obtained from an investigation of the problem in itself. We shall consider: (1) the use of reflex principles in general, and (2) some reflex principles in particular.
The Use of Reflex Principles in General. Frequently a person is in doubt as to the morality of an action that he is thinking of performing. Is there a law forbidding it, or is he morally free to perform it? In other words, which should prevail, law or liberty? His first duty, if he wishes to perform the act, is to seek direct certainty as to its morality. This he can do by examining the nature and circumstances of the action, in the light of reason, faith, and the teaching of the Church or by seeking counsel from one more learned than himself. But even when he has made such an investigation, proportionate in its thoroughness to the importance of the problem, he may still remain in doubt. He finds that there are probable reasons in favor of law and probable reasons in favor of liberty. In such a situation he may sometimes change his practical doubt into indirect or reflex certainty in favor of liberty by the use of reflex principles. (For the exceptions to this rule see morality, systems of). These are general norms of conduct, applicable to all fields of morality, enabling one to act with "the liberty of the glory of the sons of God" (Rom 8.21), without fear of formal sin, even though the action he performs may be a material sin. The basis of this doctrine is the reasonable conviction that the God of mercy and goodness does not always oblige men to obey a law binding them with any degree of probability however slight. There are different schools of thought among Catholic theologians as to the measure of probability an opinion in favor of liberty must possess before one can render it practically certain by the use of a reflex principle, but all admit the use of reflex principles to solve practical doubts of conscience in favor of liberty when the opinion for liberty possesses some particular degree of probability. (These same principles hold when a person doubts whether he is obliged to perform an act or may omit it.)
Some Reflex Principles in Particular. The best known and most widely used reflex principle is "A doubtful law does not bind" (Lex dubia non obligat ). This principle is admitted by all theologians, though it is not understood by all in the same sense. The probabilists consider a law doubtful even when the opinion for law is definitely more probable than the opinion for liberty, whereas the probabiliorists and the equiprobabilists believe that in such a case the preponderance of the opinion for law renders it practically certain.
Another reflex principle is "In a doubt the possessor is to be favored" (In dubio melior est conditio possidentis ). This principle had its origin in matters of justice, when there was a doubt as to ownership. It is reflected in a more popular form in English as "Possession is ninetenths of the law." It is used especially in equiprobabilism, when the probabilities for liberty and law are approximately equal. When the doubt concerns the existence of the law (whether there is a law, whether this person is bound by law, etc.), equiprobabilists say, liberty is in possession and may be followed; when the doubt concerns the cessation of the law (whether it has been fulfilled, whether it has been dispensed with, etc.), the law is in possession and must be obeyed.
Other reflex principles are "From what commonly occurs a prudent presumption can be drawn" (Ex communiter contingentibus prudens fit praesumptio ), and "Everything done is presumed to have been rightly done" (Omne factum praesumiter rite factum ). The former will help a person who regularly repels temptation when he is in doubt as to whether or not he has consented to a particular temptation. The latter will assist one who has made a careful general confession but who now doubts whether he has included a particular sin of the past.
Prümmer says (1:336) that all reflex principles can be reduced to this one: "In a doubt the side having the presumption is to be favored" (In dubio standum est pro quo stat praesumptio ).
See Also: doubt, moral; morality, systems of.
Bibliography: d. m. prÜmmer, Manuale theologiae moralis, ed. e. m. mÜnch (Barcelona 1945–46) 1:332–336. b. h. merkelbach, Summa theologiae moralis, 3 v. (Paris 1938) 2:85–89. alphonsus liguori, Theologia moralis, ed. l. gaudÉ, 4 v. (Rome 1905–12) 1:40–89. a. tanquerey, Synopsis theologiae moralis et pastoralis, 3 v. (new ed. Paris 1930–31) 2:419.
[f. j. connell]