(c) Light presumption occurs when the reasons are so slight, that they hardly ever suffice to permit us to infer a given fact from them. Example: If we suppose that Caius was dilatory in paying debts, and that he has no better indication of payment having been made than the fact that Titus gave him a cigar about the time of their business transaction, there is little presumption that the debt was paid. 659. Reflex principles that may be used to settle negative doubts about the quality of an act performed are the following: (a) If there is an individual presumption, the quality of the act may be inferred from what usually happens. Example: Sempronius cannot remember whether a certain good work he undertook was prompted by zeal or ambition. But, as he usually tried to keep his motives pure, it may be concluded that the work in question proceeded from a right intention. (b) If there is no individual presumption, the quality of an act may be settled from general presumptions or principles. When the act was according to law, and the doubt concerns its validity or sufficiency, one may take it that all was rightly done; for it usually happens that he who complies with the substance, also complies with what is accessory. Moreover, the welfare of the public and of individuals require that an act done outwardly according to law should be deemed as rightly performed unless the contrary can be proved. Hence the rules: “In doubt decide for the validity of what was done”; “What has been done is presumed to have been rightly done.” Examples: Caia cannot remember whether she really consented when she married Titus. Sempronius cannot remember whether he had sufficient attention in hearing Mass on Sunday. The presumptions are that Caia married validly and that Sempronius heard Mass properly, if they acted in good faith. 660. Reflex principles that may be used to settle negative and invincible doubts concerning law or obligation are the following: (a) If no serious reasons can be found to prove or disprove the existence of a law, or its gravity or application to a present case, use may be made of the principle: “Invincible ignorance of the law excuses from sin.” Example: Titus on an ember day consults all the sources of information he has to discover whether it is a fast day; but all he can learn is that some vigils are fast days, others are not. (b) If no serious reasons can be found to prove or disprove that a law bears a certain meaning, recourse may be had to such principles as the following: “A law obliges only in so far as it is knowable”; “The interpretation may be made against the legislator who could have spoken more clearly”; “Things burdensome to the subjects of the law should be construed narrowly; things favorable, broadly.” Example: Caius, who supervises workingmen, has no notion regarding the meaning of the word “workingman” as used in an indult on fasting--viz., whether it applies to supervisors of work or exclusively to laborers.