Argument from Precedent: "We Did It Before, So We Should Do It Again"

In 1954, the United States Supreme Court ruled in Brown v. Board of Education that racial segregation in public schools was unconstitutional — overturning its own 1896 precedent in Plessy v. Ferguson, which had upheld "separate but equal" facilities. The court had to argue that the precedent was wrong, that circumstances had materially changed, or both. The decision was legally and politically explosive precisely because it broke with precedent — the principle that past decisions should bind future ones. Every legal system grapples with this tension: precedent provides stability, predictability, and fairness; but rigid adherence to precedent can perpetuate injustice indefinitely. The argument from precedent is not a simple rule. It is a complex defeasible inference that requires careful analysis of what makes cases similar and what makes them different.

The Argumentation Scheme

In Douglas Walton's taxonomy, the argument from precedent takes the following form:

In case C1, action A was performed (or decision D was made).
The current case C2 is relevantly similar to C1.
Therefore, in case C2, action A should be performed (or decision D should be made).

The argument is closely related to, but distinct from, argument from analogy. The key difference: argument from precedent refers specifically to past decisions or actions as normative precedents, and derives its persuasive force from consistency and fairness — the idea that like cases should be treated alike. Argument from analogy draws on similarity between cases to transfer properties or predictions from one to another, but does not invoke the normative weight of a prior decision.

As with all argumentation schemes, the argument from precedent is defeasible: it provides a presumptive reason to act consistently with prior decisions, but this reason can be defeated by showing that the cases are not relevantly similar, that the prior decision was wrong, or that circumstances have changed in ways that make the precedent inapplicable.

Why Precedent Matters: The Case for Stare Decisis

The Latin phrase stare decisis — "to stand by things decided" — names the doctrine that courts should follow prior decisions. The doctrine is not merely a convenience; it serves several deep functions in legal and social reasoning:

• Predictability: When individuals, businesses, and institutions can rely on settled rules, they can plan their behaviour accordingly. A legal system that decides cases arbitrarily, regardless of prior decisions, fails to provide the stability that law is meant to create.
• Fairness: Treating like cases alike is a basic requirement of justice. If person A received a particular outcome in a case and person B is in an equivalent situation, giving B a different outcome is arbitrary and unfair — unless the cases are actually different in a relevant way.
• Epistemic humility: Past decisions represent the accumulated judgment of prior decision-makers who also examined the relevant facts and law. Unless there is reason to think they were specifically wrong, their conclusions deserve some deference as the product of collective deliberation.
• Efficiency: Not having to resolve every question from first principles on every occasion allows systems to function without paralysis.

Outside law, the same logic applies. Institutional policies ("we have always done X in this situation") and social conventions ("this is how we handle these cases") are functional precedents that reduce decision costs and enable coordinated action.

The Critical Questions

The argument from precedent stands or falls on its answer to three fundamental questions:

1. Similarity Question: In what respects are C1 and C2 similar? Are those similarities the relevant ones? What are the differences, and do those differences matter?
2. Correctness Question: Was the original decision in C1 actually correct — legally, morally, practically? A wrong decision is a weak foundation for a precedent.
3. Changed Circumstances Question: Have conditions changed since C1 in ways that make the precedent inapplicable or less persuasive? Does the precedent reflect a context that no longer obtains?

The similarity question is the crux. Precedents are never identical to the cases they are applied to — if they were, there would be no need for argument. The question is always which similarities and which differences are relevant — and that question requires substantive reasoning about the purpose and rationale of the original rule, not merely surface pattern-matching.

Distinguishing Precedents: When the Past Doesn't Bind

Common law legal systems have developed sophisticated techniques for limiting the reach of precedent without overruling it. The most important is distinguishing: arguing that the current case differs from the precedent in a way that is relevant to the rule the precedent established, and therefore the precedent does not apply.

The art of distinguishing requires identifying the ratio decidendi — the reason for the decision — of the prior case, as distinct from the obiter dicta (things said incidentally that were not part of the holding). Only the ratio decidendi is strictly binding. A skillful advocate can often find principled distinctions between even superficially similar cases, allowing the result to turn on the differences rather than the similarities.

This process is not mere sophistry. Good distinguishing identifies genuine differences that matter for the underlying principle at stake. Bad distinguishing invents distinctions that are formally present but substantively irrelevant — a technique used to reach preferred outcomes while maintaining the appearance of respect for precedent.

When Precedent Becomes an Obstacle: The Conservative Trap

The argument from precedent carries a structural conservative bias: it tends to preserve existing arrangements by making the burden of change fall on those who wish to change them. This is sometimes appropriate — change should be deliberate and justified. But it can also entrench historical injustices by making past decisions the default, even when those decisions reflected the biases, interests, or errors of the contexts in which they were made.

Plessy v. Ferguson illustrates the extreme case: a precedent established during the nadir of American race relations, reflecting the legal codification of white supremacy, was used for 58 years as a barrier against desegregation. Overcoming it required not just showing that the present case was different, but confronting the correctness question directly — arguing that the original decision was wrong, not merely inapplicable.

Social institutions reproduce similar patterns. "We have always excluded [group X] from [institution Y]" is an argument from precedent. It relies on the persuasive force of tradition to foreclose change without engaging the substantive question of whether the exclusion is justified. When the argument from precedent functions primarily as an argument from tradition — this is how things have been done — it merges into the appeal to tradition and loses its distinctive claim to normative weight.

Manufactured Precedent and Selective Invocation

In political and rhetorical contexts, the argument from precedent is frequently deployed in manipulative ways:

• Cherry-picking: Only the precedents that support the desired conclusion are cited; the extensive precedents pointing the other way are ignored.
• Overgeneralisation: A precedent established in a specific context is extended far beyond its original scope. "We allowed this exception once" becomes "exceptions are always permissible."
• Manufactured precedent: A practice is established with the specific intention of creating a precedent for future decisions, even when the original instance was itself unprecedented or contested.
• Guilt by association with prior cases: A proposal is rejected because it resembles a previous failure, without engaging with whether the specific causes of that failure apply to the new proposal. This merges into hasty generalisation from a single case.

Precedent vs. Innovation: When New Situations Need New Rules

A deep limitation of argument from precedent is that it requires a prior case to reason from. In genuinely novel situations — the governance of artificial intelligence, the legal status of genetic modification, the regulation of internet platforms — there may be no relevant precedent, or only weakly analogous ones that stretch uncomfortably to fit new facts.

In these contexts, argument from precedent must give way to argument from principle: reasoning about what rules should apply based on the underlying values and interests at stake, rather than what rules have been applied in superficially similar past cases. The temptation to force novel situations into pre-existing precedential categories — to regulate AI the way we regulate broadcasting, or to treat platform liability the way we treat newspaper liability — can produce frameworks that distort both the precedent and the new situation.

Sources & Further Reading

• Walton, Douglas. Methods of Argumentation. Cambridge University Press, 2013. Ch. 5: Similarity, Precedent and Argument from Analogy.
• Lamond, Grant. "Precedent and Analogy in Legal Reasoning." Stanford Encyclopedia of Philosophy, 2016. plato.stanford.edu
• Sunstein, Cass R. "On Analogical Reasoning." Harvard Law Review 106, no. 3 (1993): 741–791.
• Cross, Rupert, and J. W. Harris. Precedent in English Law. 4th ed. Oxford University Press, 1991.
• Wikipedia: Precedent, Stare decisis
• See also: Hasty Generalisation, Appeal to Emotion, Practical Reasoning, False Cause, No True Scotsman