Ronald Dworkin, answered from the texts and cited to the page.
Law as integrity is the answer, and it begins with what a judge must do when the rules run out. Judges who accept the interpretive ideal of integrity decide hard cases by trying to find, in some coherent set of principles about people's rights and duties, the best constructive interpretation of the political structure and legal doctrine of their community.1
That is the core. Not: apply the rule that fits the facts. Not: legislate from the bench when no rule fits. Rather: interpret the whole body of legal material — statutes, precedents, constitutional provisions, the long history of how courts have reasoned — so that it coheres as the expression of a single political morality, and then decide the case according to that morality.
The thought experiment of Hercules — an idealized judge of superhuman patience and information — is the device I use to make this concrete. He is not a description of how real judges work; he is the standard toward which good adjudication strives. When Hercules faces a hard case, he begins by setting out candidate interpretations of the precedents before reading them in detail: perhaps people have a moral right to compensation only for physical injury; perhaps emotional injury at the scene of an accident is covered but later emotional injury is not; perhaps recovery should track whatever rule would minimize accident costs overall.2
He then tests each candidate against two dimensions simultaneously. The first is fit: does this interpretation cohere with the bulk of what past judges actually decided? Any plausible working theory would disqualify an interpretation that denied legislative supremacy outright, or that claimed a general principle requiring the rich to share their wealth with the poor — the brute facts of legal history constrain what counts as eligible.3
The second is justification: of the interpretations that pass the fit threshold, which shows the legal practice in its best moral light? These two dimensions are not sequential steps; they constrain each other. A judge whose threshold of fit is wholly adjustable to his convictions of justice — so that his preferred moral outcome always happens to fit the precedents — is acting from bad faith or self-deception.4
The legal history genuinely checks the judge's personal convictions. That is what distinguishes law as integrity from the crude accusation that it simply lets judges impose their politics. Integrity is also not mere consistency. The adjudicative principle I call inclusive integrity requires a judge to construct his overall theory of present law so that it reflects, so far as possible, coherent principles of political fairness, substantive justice, and procedural due process, combined in the right relation.5
Sometimes proper attention to one of these virtues forces compromise in another: legislative supremacy obliges Hercules to give effect to statutes even when they produce substantive incoherence, because respecting majority lawmaking is itself a matter of fairness; strict doctrines of precedent protect citizens' reliance on past pronouncements, which is a matter of procedural due process. Pure integrity — what the law would be if judges were free simply to pursue coherence in the principles of justice flowing through all departments of law — is a more abstract ideal that inclusive integrity approximates under real institutional constraints.67
Have I, then, said what law is? Up to a point.8 I have not devised an algorithm; no computer program could take the facts and the statutes and produce a verdict everyone would accept. But I have not drawn the conclusion many readers think sensible — that there is never one right way, only different ways, to decide a hard case. That apparently sophisticated conclusion is either a serious philosophical mistake, if read as external skepticism about value, or a contentious political position resting on dubious convictions if read as global internal skepticism.9
Law as integrity consists in an approach, in questions rather than answers.10 Another judge who accepts integrity would give different answers than Hercules gives, because she would take leave of the argument at some branching point — following her own interpretive and moral convictions where they diverge from his. The question of how far I have succeeded is therefore a distinct question for each reader: how far along the tree of argument would she follow me, given the convictions she finds she has after the reflection I have tried to provoke?11
Judges who accept the interpretive ideal of integrity decide hard cases by trying to find, in some coherent set of principles about people's rights and duties, the best constructive interpretation of the political structure and legal doctrine of their community.Law's Empire, p. 273
He begins by setting out various candidates for the best interpretation of the precedent cases even before he reads them. Suppose he makes the following short list: (1) No one has a moral right to compensation except for physical injury. (2) People have a moral right to compensation for emotional injury suffered at the scene of an accident against anyone whose carelessness caused the accident but have no right to compensation for emotional injury suffered later. (3) People should recover compensation for emotional injury when a practice of requiring compensation in their circumstances would diminish the overall costs of accidents or otherwise make the community richer in the long run.Law's Empire, p. 258
Convictions about fit will provide a rough threshold requirement that an interpretation of some part of the law must meet if it is to be eligible at all. Any plausible working theory would disqualify an interpretation of our own law that denied legislative competence or supremacy outright or that claimed a general principle of private law requiring the rich to share their wealth with the poor.Law's Empire, p. 273
If his threshold of fit is wholly derivative from and adjustable to his convictions of justice, so that the latter automatically provide an eligible interpretation—then he cannot claim in good faith to be interpreting his legal practice at all. Like the chain novelist whose judgments of fit automatically adjusted to his substantive literary opinions, he is acting from bad faith or self-deception.Law's Empire, p. 273
The adjudicative principle that governs our law enforces inclusive integrity: this requires a judge to take account of all the component virtues. He constructs his overall theory of the present law so that it reflects, so far as possible, coherent principles of political fairness, substantive justice, and procedural due process, and reflects these combined in the right relation.Law's Empire, pp. 423–424
Legislative supremacy, which obliges Hercules to give effect to statutes even when these produce substantive incoherence, is a matter of fairness because it protects the power of the majority to make the law it wants. Strict doctrines of precedent, the practices of legislative history, and local priority are largely, though in different ways, matters of procedural due process because they encourage citizens to rely on doctrinal pronouncements and assumptions that it would be wrong to betray in judging them after the fact.Law's Empire, pp. 423–424
Pure integrity abstracts from these various constraints of fairness and process. It invites him to consider what the law would be if judges were free simply to pursue coherence in the principles of justice that flow through and unite different departments of law.Law's Empire, pp. 423–424
Have I said what law is? The best reply is: up to a point. I have not devised an algorithm for the courtroom.Law's Empire, pp. 430–431
I have not said that there is never one right way, only different ways, to decide a hard case. On the contrary, I said that this apparently worldly and sophisticated conclusion is either a serious philosophical mistake, if we read it as a piece of external skepticism, or itself a contentious political position resting on dubious political convictions if we treat it, as I am disposed to do, as an adventure in global internal skepticism.Law's Empire, pp. 430–431
law as integrity consists in an approach, in questions rather than answers, and other lawyers and judges who accept it would give different answers from his to the questions it asks.Law's Empire, p. 258
The question how far I have succeeded in showing what law is is therefore a distinct question for each reader. He must ask how far he would follow me along the tree of argument, given the various interpretive and political and moral convictions he finds he has after the reflection I have tried to provoke.Law's Empire, pp. 430–431