"A law is laid down as a rule or measure of human acts. Now a measure ought to be homogeneous with the thing measured. Hence laws also must be imposed upon men according to their condition. As Isidore says: 'A law ought to be possible both according to nature and according to the custom of the country.' Now the power or faculty of action proceeds from interior habit or disposition. The same thing is not possible to him who has no habit of virtue, that is possible to a virtuous man; as the same thing is not possible to a boy and to a grown man, and therefore the same rule is not laid down for children as for adults. Many things are allowed to children, that in adults are visited with legal punishment or with blame, and in like manner many things must be allowed to men not perfect in virtue, which would be intolerable in virtuous men." This reasoning leads us up to a conclusion, which St. Thomas states thus (la 2æ, q. 94. art. 5): "A conceivable way in which the Natural Law might be changed is the way of subtraction, that something should cease to be of the Natural Law that was of it before. Understanding change in this sense, the Natural Law is absolutely immutable in its first principles; but as to secondary precepts, which are certain detailed conclusions closely related to the first principles, the Natural Law is not so changed as that its dictate is not right in most cases steadily to abide by; it may however be changed in some particular case, and in rare instances, through some special causes impeding the observance of these secondary precepts." The reason for this conclusion, more pregnant, it may be, than St. Thomas himself discerned, is given briefly as follows (2a 2æ, q. 57, art. 2, ad 1): "Human nature is changeable; and therefore what is natural to man may sometimes fail to hold good." The precepts of Natural Law that fail to be applicable when human nature sinks below par, are only secondary precepts, and few even of them. Christianity brings human nature up to par, and _fulfils_ the Natural Law (St. Matt. v. 17), enjoining the observance of it in its integrity. This is the meaning of St. John Chrysostom's saying: "Of old not such an ample measure of virtue was proposed to us; ... but since the coming of Christ the way has been made much narrower." (_De Virginitate_, c. 44: cf. his 17th Homily on St. Matt. v. 37; indeed the doctrine is familiar in his pages.) Thus the prohibition of polygamy, being a secondary precept of the natural law, failed in its application in that age of lapsed humanity, when a woman was better one of many wives, protected by one husband, than exposed to promiscuous violence and lust. (Isaias iv. i.) NOTE ON ROUSSEAU. The ruler is the servant of the _good_ of the people, not of the _will_ of the people, except inasmuch as-- a. the _will_ of the people is an indication of their _good_, of which they are probable judges;