Is Law Based on Logic

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Since Justice Holmes asserted that „the life of law is not logical, but experience,“ lawyers and judges in the United States have downplayed the importance of formal logic in understanding law and legal thought. Many jurists and practitioners feared that recognizing that logic is at the heart of law risked returning to the rationalist excesses of formalist jurisprudence that dominated nineteenth-century legal thought. It is, after all, against this formalist tradition that Holmes wrote. And it was in stark opposition to this tradition that members of the realist legal movement in America, as well as the free rights movement in Europe, directed much of their energies in the early twentieth century. Essentially, the field of law, and perhaps especially the practice of judicial decision-making, are exercises in practical thinking. There is certainly more to law than logic. However, the myriad of factors that contribute to good legal practice and fair judgment suggest that the „life of the law,“ while not just logical, is a variety of activities, all of which use and depend on reason in specialized ways. The level of detail required when drafting contracts, wills, trusts and other legal documents is rational precision; The care that litigators must take in planning and strategy in deciding how to present their case is rational diligence; The written and oral reasoning required for the practice of appeal is obviously a rational ability; the talent expected of administrative judges to produce consistent findings of fact and legal conclusions is a rational talent; And the ability of trial and appellate judges to impartially and impartially separate the core reasoning from rhetorical and emotional chaff from adversarial representation in order to render legally justified judgments is a rational skill. But somewhere between strict formalist jurisprudence and utter disregard for logic and argumentative form, law and judicial practice truly find peace. Although all that is usually repeated by Justice Holmes is the concise remark quoted above, his jurisprudential writings, as well as his legal opinions, make it clear that it was never his intention to pretend that logic is not a central aspect of law or judicial decision-making. He, along with legal realists and other critics of legal formalism, have recognized that evaluation and the creation of arguments are at the heart of the lawyer`s judgment. This article discusses the legal applications of logic, with a particular focus on logic models of legal reasoning.

We argue that the law is a rich testing ground and an important field of application for logic-based AI research. The initial applications of logic to the presentation of legislation are reviewed, with an emphasis on representation and the legal conclusions that emerge from this presentation as a derivation. This includes the presentation of deontic concepts, normative positions, legal ontologies, time and change. Then the legal applications of logic are reviewed, where legal rules are not only applied, but are the subject of argumentation and discourse. This includes discussing the application of legislation in unforeseen circumstances, interpreting reasoning in light of the facts of a case, and providing evidence to establish the facts of a case. This part of the review places particular emphasis on argument-based approaches. This also applies to the last part, which deals with formal models of legal procedure and multi-agent interaction in court proceedings. The review concludes with the identification of some of the key open research questions.

The review shows that modern legal applications of logic confirm the recent tendency to extend the scope of deduction logic to the flow of information, reasoning, and interaction. Equally important is a second basic category of reasoning – deductive logic, especially the forms of deductive arguments known as „syllogisms.“ These are the classic forms of the deductive argument, which consist of a main premise, a secondary premise, and a conclusion. It was this aspect of logic that provoked such virulent opposition to formalism a century ago. And it is this aspect of logic that has been so downplayed throughout the twentieth century. Yet even a rudimentary understanding of deductive logic gives lawyers, judges, and law students a valuable tool for determining whether an argument in a legal opinion or brief is valid or misleading.