Louis Brandeis asked "has not the recent dissatisfaction with our law as administered been due, in large measure, to the fact that it had not kept pace with the rapid development of our political, economic, and social ideals? In other words, is not the challenge of legal justice due to its failure to confirm to contemporary conceptions of social justice?" ... [unlike] " [p]olitical as well as economic and social science [that] noted these revolutionary changes ... legal science -- the unwritten or judge-made laws as distinguished from legislation -- was largely deaf and blind to them." [Louis D. Brandeis, "The Living Law" (1916)].

Following in the tradition of Pound and Brandeis, Justice Cardozo introduced the need to adapt law to society to his theory of adjudication. Cardozo suggested that "the problem which confronts the judge is in reality a twofold one: he must first extract from the precedents the underlying principle, the ratio decidendi; he must then determine the path or direction along which the principle is to move and develop if it is not to wither and die ... The directive force of a principle may be exerted along the line of logical progression; this ... [he called] ... the rule of analogy or the method of philosophy; along the line of historical development; this ... [he called] ... the method of evolution; along the line of the customs of the community; this ... [he called] ... the method of tradition; along the lines of justice, morals and social welfare, the mores of the day; and this ... [he called] ... the method of sociology ... The judicial process is there in microcosm. We go forward with our logic, with our analogies, with our philosophies, till we reach a certain point. At first, we have no trouble with the paths; they follow the same lines. Then they begin to diverge, and we must make a choice between them. History or custom or social utility or some compelling sentiment of justice or sometimes perhaps spirit of our law must come to the rescue of the anxious judge, and tell him where to go."

Having explored the methods of philosophy, history and custom, Cardozo went on to suggest that "the force which in our day and generation is becoming the greatest of them all, the power of social justice which finds its outlet and expression in the method of sociology.

The final cause of law is the welfare of society. The rule that misses its aim cannot permanently justify its existence. ‘Ethical considerations can no more be excluded from the administration of justice which is the end and purpose of all civil laws than one can exclude the vital air from his room and live.’ Logic, and history and custom have their place. We will shape the law to conform to them when we may; but only within bounds. The end which the law serves will dominate them all ... I do not mean, of course, that judges are commissioned to set aside existing rules at pleasure in favor of any other set of rules which they may hold to be expedient or wise. I mean that when they are called upon to say how far existing rules are to be extended or restricted, they must let the welfare of society fix the path, its direction and its distance....

.... [J]udges are not commissioned to make and unmake rules at pleasure in accordance with changing views of expediency or wisdom... Nearer to the truth for us are the words of an English judge: ‘Our common law system consists in applying to new combinations of circumstances those rules of law which we derive from legal principles and judicial precedents, and for the sake of attaining uniformity, consistency and certainty, we must apply those rules when they are not plainly unreasonable and inconvenient to all cases which arise; and we are not at liberty to reject them and to abandon all analogy to them in those in which they have not yet been judicially applied, because we think that the rules are not as convenient and reasonable as we ourselves could have devised.’ This does not mean that there are not gaps, yet unfilled, within which judgment moves untrammeled. Mr. Justice Holmes has summed it up in one of his flashing epigrams: ‘I recognize without hesitation that judges must and do legislate, but they do so only interstitially; they are confined from molar to molecular motions. A common-law judge could not say, I think the doctrine of consideration a bit of historical nonsense and shall not enforce it in my court.’ This conception of the legislative power of a judge as operating between spaces is akin to the theory of ‘gaps in the law’ familiar to foreign jurists... What concerns us now, however, is not the size of the gaps. It is rather the principle that shall determine how they are to be filled, whether their size be great or small. The method of sociology in filling the gaps puts its emphasis on the social welfare.

Social welfare is a broad term ... It may mean what is commonly spoken as public policy, the good of the collective body. In such cases, its demands are often those of mere expediency or prudence. It may mean on the other hand the social plan that is wrought by adherence to the standards of right conduct, which find expression in the mores of the community. In such cases, its demands are those of religion or of ethics or of the social sense of justice, whether formulated in creed or system, or immanent in the common mind. One does not readily find a single term to cover these and kindred aims which shade off into one another by imperceptible gradations.....

... [T]oday in every department of the law ... the social value of a rule has become a test of growing power and importance. ... [As Pound noted] ...‘Perhaps the most significant advance in the modern science of law is the change from the analytical to the functional attitude.’ ‘The emphasis has changed from the content of the precept and the existence of the remedy to the effect of the precept in action and the availability and efficiency of the remedy to attain the ends for which the precept was devised.’ ...

Cardozo conceded "that the rule of adherence to precedent, though it ought not to be abandoned, ought to be in some degree relaxed." Still, he argued, "that when a rule, after it has been duly tested by experience, has been found to be inconsistent with the sense of justice or with the social welfare, there should be less hesitation in frank avowal and full abandonment. We have had to do this sometimes in the field of constitutional law. Perhaps we should do so oftener in fields of private law where considerations of social utility are not so aggressive and insistent. There should be greater readiness to abandon an untenable position when the rule to be discarded may not reasonably be supposed to have determined the conduct of the litigants, and particularly when in its origin it was the product of institutions or conditions which have gained a new significance or development with the progress of the years." [Benjamin N. Cardozo, The Nature of the Judicial Process (1921), 28, 30-31, 43, 65-73].