§ 68 The Sources of Judicial Principles
Whence, then, do the courts derive those new principles, or rationes decidendi, by which they supplement the existing law? They are in truth nothing else than the principles of natural justice, practical expediency, and common sense. Judges are appointed to administer justice—justice according to law, so far as the law extends, but so far as there is no law, then justice according to nature. Where the civil law is deficient, the law of nature takes its place, and in so doing puts on its character also. But the rules of natural justice are not always such that any man may know them, and the light of nature is often but an uncertain guide. Instead of trusting to their own unguided instincts in formulating the rules of right and reason, the courts are therefore wisely in the habit of seeking guidance and assistance elsewhere. In establishing new principles, they willingly submit themselves to various persuasive influences which, though destitute of legal authority, have a good claim to respect and consideration. They accept a principle, for example, because they find it already embodied in some system of foreign law. For since it is so sanctioned and authenticated, it is presumably a just and reasonable one. In like manner the courts give credence to persuasive precedents, to judicial dicta, to the opinions of text-writers, and to any other forms of ethical or juridical doctrine which seem good to them. There is, however, one source of judicial principles which is of special importance, and calls for special notice. This is the analogy of pre-existing law. New rules are very often merely analogical extensions of the old. The courts seek as far as possible to make the new law the embodiment and expression of the spirit of the old—of the ratio juris, as the Romans called it. The whole thereby becomes a single and self-consistent body of legal doctrine, containing within itself an element of unity and of harmonious development. At the same time it must be remembered that analogy is lawfully followed only as a guide to the rules of natural justice. It has no independent claim to recognition. Wherever justice so requires, it is the duty of the courts, in making new law, to depart from the ratio juris antiqui, rather than servilely to follow it.
It is surprising how seldom we find in judicial utterances any explicit recognition of the fact that in deciding questions on principle, the courts are in reality searching out the rules and requirements of natural justice and public policy. The measure of the prevalence of such ethical over purely technical considerations is the measure in which case-law develops into a rational and tolerable system as opposed to an unreasoned product of authority and routine. Yet the official utterances of the law contain no adequate acknowledgment of this dependence on ethical influences. “The very considerations,” it has been well said, “which judges most rarely mention, and always with an apology, are the secret root from which the law draws all the juices of life.”168 The chief reason of this peculiarity is doubtless to be found in the fictitious declaratory theory of precedent, and in the forms of judicial expression and reasoning which this theory has made traditional. So long as judges affect to be looking for and declaring old law, they cannot adequately express the principles on which they are in reality making new.