Substantive due process is a judicial doctrine used to review the content of laws, not just the fairness of procedures. It asks whether government has crossed constitutional limits by burdening liberty in an unjustified way.

Core Idea: Due Process as a Limit on Arbitrary Power

What substantive due process does

Substantive due process allows courts to invalidate laws when their substance is so unjustified that it violates constitutional protections for liberty. Unlike procedural due process (which focuses on fair steps), this doctrine examines whether the government may regulate a particular activity at all, or only under certain conditions.

The underlying concern is preventing arbitrary laws—rules that are not meaningfully connected to a legitimate governmental purpose or that intrude too deeply into protected spheres of individual freedom.

Constitutional Foundations and Scope

Textual basis

Substantive due process is rooted in the due process clauses:

A side-by-side visual emphasizing that the U.S. Constitution contains due process language in both the Fifth Amendment (binding the national government) and the Fourteenth Amendment (binding states). This supports the idea that substantive due process is anchored in constitutional text about deprivation of “life, liberty, or property” and helps students remember the federal/state split. The image is useful as a quick “where it comes from” reference before moving into standards of review. Source

• Fifth Amendment (limits the national government)

• Fourteenth Amendment (limits state and local governments)

The key phrase is “life, liberty, or property” and the constitutional requirement that government may not deprive people of these without due process of law.

What courts are evaluating

In substantive due process cases, the Court typically asks:

• What liberty interest is being burdened?

• Is that interest treated as especially protected (often described as fundamental)?

• How strong is the government’s justification, and how closely does the law fit that justification?

How the Court Checks for “Arbitrary” Laws

Step 1: Identify the liberty interest at stake

Courts first characterise what the law restricts. This framing matters because it influences whether the Court treats the interest as highly protected or as ordinary regulation.

Step 2: Choose a standard of review

A comparative diagram of the three major judicial scrutiny standards used in constitutional review. It shows how rational basis is the most deferential (requiring a legitimate interest and a rational relationship), intermediate scrutiny is more demanding (important interest and substantial relationship), and strict scrutiny is the most demanding (compelling interest and narrow tailoring). This helps connect substantive due process analysis to the broader “levels of scrutiny” framework courts use when evaluating government justifications. Source

The Court applies different levels of scrutiny depending on the interest involved. These standards operationalise the idea in the syllabus: checking whether government action arbitrarily infringes rights.

• Rational basis review (most deferential)

  • Government must show a legitimate objective.

  • The law must be rationally related to that objective.

  • Many laws survive because the Court presumes constitutionality and allows broad policymaking discretion.

• Heightened protection for fundamental liberty interests (more demanding review)

  • Government generally must show a very strong objective and a tight fit between means and ends.

  • The Court is less tolerant of speculative, moralistic, or overly broad reasoning when the burden on liberty is severe.

Step 3: Evaluate fit, overbreadth, and justification

Even when government goals are permissible, substantive due process analysis often focuses on whether the law is:

• Overinclusive (sweeps in a lot of harmless conduct)

• Underinclusive (claims to address a problem but leaves major sources untouched)

• Poorly tailored (uses a blunt tool when less restrictive options could serve the same end)

• Pretextual (asserts one purpose while effectively pursuing another)

Why Substantive Due Process Is Controversial (But Exam-Relevant)

Competing constitutional values

Substantive due process reflects a tension between:

• Judicial protection of liberty (preventing majorities from enacting oppressive or arbitrary rules), and

• Democratic self-government (elected lawmakers making policy choices without judges substituting their preferences)

Common critiques you should recognise

• Text and legitimacy critique: Skeptics argue the Constitution does not explicitly authorise judges to protect certain liberties from regulation.

• Indeterminacy critique: Critics warn that “fundamental” liberty can be defined too flexibly, enabling inconsistent outcomes.

• Rights-protection defence: Supporters argue that “liberty” has real substance and that courts must enforce constitutional limits when politics fails to protect individuals.

Practical limits

Even when applying substantive due process, the Court usually:

• Gives legislatures room to regulate in areas of health, safety, and welfare

• Requires strong reasons before overriding policymaking choices

• Treats many disputes as best resolved through ordinary politics unless a significant liberty interest is clearly burdened