Aldisert, R J; Clowney, S; Peterson, J D --- "Logic for Law Students: How to Think Like a Lawyer" [2007] LegEdDig 36; (2007) 15(2) Legal Education Digest 48

Logic for Law Students: How to Think Like a Lawyer

R J Aldisert, S Clowney & J D Peterson

[2007] LegEdDig 36; (2007) 15(2) Legal Education Digest 48

68 U Pitt L R 2, 2007, pp 100–121

Logic anchors the law. The law’s insistence on sound, explicit reasoning keeps lawyers and judges from making arguments based on untethered, unprincipled, and undisciplined hunches. Traditionally, logicians separate the wider universe of logical reasoning into two general categories: inductive and deductive. Defined broadly, deduction is reasoning in which a conclusion is compelled by known facts.

The specific form of deductive reasoning that you will find lurking below the surface of most judicial opinions and briefs is the syllogism — a label logicians attach to any argument in which a conclusion is inferred from two premises.

According to the traditional jargon, the syllogism’s three parts are called the major premise, the minor premise, and the conclusion. The major premise states a broad and generally applicable truth. The minor premise states a specific and usually more narrowly applicable fact. The conclusion then draws upon these premises and offers a new insight that is known to be true based on the premises.

It is no exaggeration to say that the syllogism lies at the heart of legal writing.

We urge all law students to get in the habit of thinking in syllogisms. When briefing a case as you prepare a class assignment, the skeleton of the deductive syllogism should always poke through in your description of the case’s rationale.

But how, you might ask, does a new lawyer learn to construct valid syllogisms?

If you find yourself having trouble organising a brief or memo, try shoehorning your argument into this generic model, which is based on the argument made by prosecutors in nearly every criminal case:

Major premise: [Doing something] [violates the law.]

Minor premise: [The defendant] [did something.]

Conclusion: [The defendant] [violated the law.]

But wait! — you might be thinking — this syllogism business is too simple: opinions and memos are never so straightforward. Well, yes and no. The syllogism is simple, and indeed it does undergird most legal arguments, but sometimes you have to dig a bit below the surface to excavate syllogisms.

Sometimes a legal writer doesn’t mention all parts of the syllogism, leaving you to read between the lines. Logicians are certainly aware that an argument can be founded on a syllogism although not all parts of the syllogism are expressed. They even have a name for such an argument: an enthymeme. Often, enthymemes are used for efficiency’s sake. If a premise or conclusion is obvious, then the writer can save her precious words to make less obvious points.

In addition to note handling the reader syllogisms on a platter, legal writers also have the tendency to pile one syllogism on top of another. Not surprisingly, logicians have a term for this, too, but for once it is a term that makes sense and is easy to remember: a series of syllogisms in which the conclusion of one syllogism supplies a premise of the next syllogism is known as a polysyllogism. Typically, polysyllogisms are used because more than one logical step is needed to reach the desired conclusion.

You have been warned: watch for enthymemes and polysyllogism in every opinion or legal memo or brief that you read, and be aware of them in your own writing. Your arguments will be improved. A syllogism is a powerful tool because of its rigid inflexibility. If the premises of a syllogism are properly constructed, the conclusion must follow. But beware of bogus arguments masquerading as syllogism.

Certain buzzwords, however, can help distinguish valid syllogisms from fallacious ones. Alarm bells should sound immediately if you spot terms in the major premise like ‘some’, ‘certain’, ‘a’, ‘one’, ‘this’, ‘sometimes’, ‘many’, ‘occasionally’, ‘once’, or ‘somewhere’. Remember at all costs: the principle behind the syllogism is that what’s true of the universal is true of the specific. In deductive reasoning, you reason from the general to the particular. Accordingly, if you’re unsure about the nature of the general, you can’t draw proper conclusions about the particular.

Certain logical errors crop up again and again, and so you should take particular care to avoid them: Don’t cite inappropriate secondary authorities or cases from outside jurisdictions; logicians consider that an appeal to inappropriate authority. Don’t rely on attacks on your opponents’ character. Don’t rely on appeals to emotion. Don’t rely on fast talking or personal charm to carry the day. A cool head coupled with rigorous legal research turns a case in your favour, not rhetorical tricks.

It is critical to read every legal document you come across with care. Bad reasoning can seem persuasive at first glance. Logical fallacies are especially hard to spot in briefs, memos, and court opinions because of the dense writing and complex fact patterns. Yet the effort is worthwhile. The ability to detect and avoid logical missteps will improve your writing immensely, and develop your ability to ‘think like a lawyer’ — the skill that professors and partners so admire.

Where an issue of law is unsettled and there is no binding precedent to supply a major premise for your syllogism, deductive logic is of no use to you. By focussing on such cases, your professors will drag you kicking and screaming into the land of induction, the second category of logic.

Inductive generalisation is a form of logic in which big, general principles are divined from observing the outcomes of many small events. In this form of inductive logic, you reason from multiple particulars to the general.

The contrast with deductive reasoning is stark. Whereas syllogisms are mechanical and exact — if the premises are true and properly assembled, the conclusion must be true — inductive logic is not so absolute. It does not produce conclusions guaranteed to be correct, no matter how many examples scholars assemble. Thus, inductive reasoning is a logic of probabilities and generalities, not certainties. It yields workable rules, but not proven truths.

The absence of complete certainty, however, does not dilute the importance of induction in the law. As we stated at the outset, we look to inductive reasoning when our legal research fails to turn up a hefty, hearty precedent that controls the case. When there is no clear statute — no governing authority — to provide the major premise necessary for a syllogism, the law student must provide the major premise necessary for a syllogism, the law student must build the major premise himself.

Inductive generalisations, then, are easy enough to understand. You can get in trouble using them, however. Most importantly, you must be careful to assemble a sufficient number of examples before shaping a far-reaching rule, or you will be guilty of the Fallacy of Hasty Generalisation. In logic-speak this fallacy occurs when you construct a general rule from an inadequate number of particulars.

The difficulty comes in knowing how many instances are sufficient to make a generalisation. Three? Ten? Forty Thousand? This is where the art comes in. As a rule of thumb, the more examples you find, the stronger your argument becomes. Raw numbers are not enough to give you a reliable generalisation, however. Consider this classic blunder: In 1936, Literary Digest magazine conducted a massive polling effort to predict the outcome of the Presidential election between Alf Landon and Franklin Roosevelt. The Digest polled well over two million people, and the vast majority indicated they would vote for Landon. In the actual election, however, Roosevelt won 523 electoral votes and Landon received only eight. How did Literary Digest get it so wrong when it had crafted its rule from a massive number of particular examples? It seems the Digest had focused its polling efforts on car owners — an unrepresentative group of the American public in 1936. From this example it should become clear that the strength of an inductive argument rests not only on the number of examples you turn up to support your generalisation, but also on the representatives of the sample size. Keep this in mind when your opponent makes an argument based solely on the use of statistics, as is the case in many antitrust, securities, and discrimination claims.

You will never completely escape the risks posed by the fallacy of hasty generalisation. We can never know with certainty that an inductive generalisation is true. The best that can be hoped for is that expert research and keen attention to statistics will divine workable rules that are grounded in the wisdom of human experience. Notwithstanding its shortcomings, the inductive generalisation remains a vital tool because the ability to shape persuasive legal arguments when no clear precedent exists is often what separates a star attorney from your run-of-the-mill ambulance chaser.

Anyone who has struggled through a first-year torts course knows that hypothetical questions play a central role in the law school classroom. Professors invent elaborate factual scenarios and ask students to distil the correct result from a handful of cases read the night before. Then they change the situation slightly; does the answer change? Now alter a different parameter — same result, or a different one? The imaginative fact patterns do not end with law school; judges too rely on outlandish hypotheticals to test the validity of lawyer’s argument. Yet, notwithstanding the importance of hypothetical questions in legal thinking, the ability to manage them remains poorly taught and rarely practiced. We believe that the careful use of analogy — a form of inductive reasoning — can get you past a nasty hypothetical.

Edward Levi, the foremost American authority on the role of analogy in the law, described analogical reasoning as a three step process: (1) establish similarities between two cases; (2) announce the rule of law embedded in the first case; and (3) apply the rule of law to the second case. This form of reasoning is different from deductive logic or inductive generalisation. Recall that deduction requires us to reason from universal principles to smaller, specific truths. And the process of generalisation asks us to craft larger rules from a number of specific examples. Analogy, in contrast, makes one-to-one comparisons that require no generalisations or reliance on universal rules. In the language of logicians, analogy is a process of reasoning from the particular to the particular.

A proper analogy should identify the respects in which the compared cases, or fact scenarios, resemble one another and the respects in which they differ. What matters is relevancy — whether the compared traits resemble, or differ from, one another in relevant respects. A single apt comparison can be worth more than a host of not-quite-right comparisons.

The Court of Appeals for the Third Circuit discussed all of these principles in detail in an important class action antitrust case where the principal issue on appeal was whether the holding in a case called Newton applied to the case at bar:

For Appellants’ argument to prevail, therefore, they must demonstrate that the facts in Newton are substantially similar to the facts in the case at bar, what logicians call inductive reasoning by analogy, or reasoning from one particular case to another. To draw an analogy between two entities is to indicate one or more respects in which they are similar and thus argue that the legal consequence attached to one set of particular facts may apply to a different set of particular facts because of the similarities in the two sets. Because a successful analogy is drawn by demonstrating the resemblances or similarities in the facts, the degree of similarity is always the crucial element.

Logicians teach that one must always appraise an analogical argument very carefully. Several criteria may be used: (1) the acceptability of the analogy will vary proportionally with the number of circumstances that have been analysed; (2) the acceptability will depend upon the number of positive resemblances (similarities) and negative resemblances (dissimilarities); or (3) the acceptability will be influenced by the relevance of the purported analogies.

For Appellants to draw a proper analogy, they had the burden in the district court, as they do here of showing that the similarities in the facts of the two cases outweigh the differences. They cannot do so, for two significant reasons.

Firstly, in Newton it was clear that not all members of the putative class sustained injuries; here, all members sustained injuries because of the artificially increased prices. Secondly, in Newton there were hundreds of millions of stock transactions involved, thus making the putative class extremely unmanageable; here, an astronomical number of transitions is not present.

You may find the discipline of parsing legalese into logical forms to be time-consuming and arduous at first, but as you become more comfortable with logic’s frameworks, you will find that the exercise helps you more efficiently peel a case back to its essence. A solid footing in logic will help you feel more secure when you find yourself in a complex doctrinal thicket. And while the fundamentals of logic laid out in the article will not give you a magic carpet on which you can float above the legal briar patch, we believe they will give you a machete that will help you start hacking your way through the tangle.