Induction and Deduction in Legal Reasoning

A legal example from the field. Two hundred and seventeen productions observed, information given in thirty-one, and the inference that the practice in that court is not to inform.

Its virtue. It produces something new. Every general proposition in a case law field was inferred from instances.

Its limits.

The conclusion is probable, never certain. The next instance may differ.

It depends on the sample. An induction from unrepresentative instances is unsound, which is why chapters 1000 to 1020 exist.

And it can be defeated by a single counter-instance, which is why the search for contrary authority is part of testing, chapter 1160.

Where each is used in legal research

Ascertaining the law from a statute: deductive. The rule is given and applied.

Ascertaining the law from cases: inductive, then deductive. The ratio of each decision is extracted, a principle is inferred from the line, and the principle is then applied to the facts in hand. This two step movement is what a law student does every day without naming it.

Distinguishing a case: testing an induction. To distinguish is to say that the general proposition inferred does not extend to these facts.

Empirical research: inductive throughout. Observations produce a proposition about a population, and the proposition is probable within stated limits.

Formulating a hypothesis: usually deductive in derivation and inductive in test. The expectation is deduced from a theory or from a rule's own assumption, chapter 1130, and it is tested against instances.

And law reform: inductive from findings, deductive to the remedy. A cause is inferred from cases observed, and the remedy is deduced from what the law empowers a body to do, chapter 1420.

The two together, which is the answer an examiner wants

Neither alone is sufficient and legal reasoning alternates between them.

A worked alternation. A researcher reads twenty decisions on when a Lok Adalat award may be questioned, infers inductively that the courts will interfere only where there was no genuine compromise, deduces from that proposition what should happen in a new case where a party says he never agreed, tests the deduction against the next decision found, and revises the induction if it fails.

That cycle is the whole of doctrinal method, chapter 840, and it is worth saying so in an answer because most candidates present induction and deduction as two separate things a researcher chooses between.

The related distinctions worth naming

Analogy. Reasoning from one particular to another particular because they resemble each other in a material respect. This is what a court does when it applies a case, and it is neither purely inductive nor purely deductive.

Abduction, or inference to the best explanation. Given a finding, the researcher asks what would best explain it. The four candidate causes of chapter 740 are abductive, and abduction generates hypotheses which are then tested.

And logic against truth. Logic tests whether a conclusion follows; it cannot tell you whether the premises are true, which is why the sources matter, chapter 920.

Social values, morality and logic

A question asked on one of the papers puts these three together, and they belong together for a reason.

Logic governs the form of an argument and is silent about its content.

The premises come from the law, chapter 1050, and from the values the law itself expresses: Article 39A's equal opportunity, the fair procedure requirement of Article 21.

And morality enters where the law is silent or where a choice must be made between two defensible readings. A researcher recommending a reform is making a value judgment and should say so rather than presenting it as a deduction, chapter 900.

The honest position for a legal researcher. Reason validly; take the premises from the sources; and where a value premise is being supplied, name it. That single discipline answers the whole of this question.

A worked example

One problem, reasoned both ways.

The question. Must a magistrate inform an accused of the right to free legal services at the second remand as well as the first?

Deductively. Major premise, from Khatri: the obligation arises when the accused is first produced before the magistrate and at every remand. Minor premise: this is a remand. Conclusion: the obligation arises. Certain, if the premise is accurately stated, which is why it was read in full text.

Inductively. Suppose the researcher has observed sixty first productions and sixty later remands and finds that information was given in eleven of the first and in one of the second. The inference is that the practice, where it exists at all, attaches to the first production only.

Now notice what the two produce together. The deduction gives the legal position; the induction gives the practice; and the gap between them is the finding, chapter 680. Neither method alone produces it.

Quick revision

Deduction: general to particular; the conclusion follows necessarily if the premises are true; classical form is the syllogism. It adds nothing, is only as good as the major premise, and the real argument is usually in the minor premise. Validity is form; truth is content.

Induction: particular to general; the conclusion is probable; it produces something new; it depends on the representativeness of the instances and can be defeated by a counter-instance.

Where each is used: statute is deductive; case law is inductive then deductive; distinguishing tests an induction; empirical work is inductive throughout; a hypothesis is deduced and tested inductively; and reform infers the cause and deduces the remedy.

They alternate, and saying so is the answer an examiner wants.

Related: analogy, particular to particular; abduction, inference to the best explanation, which generates hypotheses; and the point that logic cannot supply true premises.

Values and morality enter through the premises, and a researcher supplying a value premise must name it.

Test yourself

1. Define induction and deduction and state the difference in the certainty of the conclusion. Deduction reasons from a general proposition to a particular case, and if the premises are true and the reasoning valid the conclusion must be true. Induction reasons from observed particular instances to a general proposition, and the conclusion is probable rather than certain, since the next instance may differ.

2. Show how a law student uses both in reading case law. Inductively first, by extracting the ratio of each decision and inferring a general principle from the line of authority; then deductively, by applying that principle to the facts in hand. Distinguishing a case is a test of the induction, since it asserts that the inferred proposition does not extend to these facts.

3. What is the practical weakness of a deductive legal argument, and where does the real dispute lie? That it adds nothing new and is only as reliable as its major premise, so an amended or overruled source destroys the whole chain. The real dispute usually lies in the minor premise, namely whether the facts of the case fall within the rule, which is not itself a deductive question.

4. How do social values and morality enter legal reasoning, and what does a researcher owe? Through the premises. Logic governs only the form of an argument and is silent about content; the premises come from the sources and from the values the law itself expresses, and where the law is silent or two readings are defensible a value premise must be supplied. The researcher owes it to the reader to name that premise rather than to present a value judgment as a deduction.