This article was originally written as the script for an episode of my podcast Reasoned Talk. But the concepts were too complex and the cases too numerous for an audio program, so I abandoned the recording and edited the script into an article instead.

On the afternoon of May 17, 1954, in Washington, D.C., the nine Justices of the Supreme Court filed into the courtroom. The newly appointed Chief Justice, Earl Warren, picked up an opinion and began to read.

The decision was only eleven pages long, yet it profoundly changed American history. Warren wrote:

Separating Black children from others of similar age and qualifications solely because of race creates a sense of inferiority about their place in society. That feeling may affect their hearts and minds in ways that may never be undone.

At the end of the opinion, the Court rejected in one concise sentence a policy that had endured for more than half a century:

In public education, the doctrine of “separate but equal” has no place. Separate educational facilities are inherently unequal.

This was Brown v. Board of Education, one of the most important decisions in American constitutional history. It destroyed the constitutional foundation of racial segregation in public schools. Of course, one judicial opinion did not make segregation disappear overnight. Southern states resisted for years afterward. But from that day on, the legal legitimacy of segregated public schools was gone.

The constitutional text supporting that decision was the celebrated Fourteenth Amendment.

I have mentioned the Fourteenth Amendment repeatedly in previous episodes because it is the foundation of birthright citizenship in the United States. Yet its significance reaches far beyond birthright citizenship. Some have called it America’s “Second Constitution,” and it was one of the most important achievements of the country’s “Second Founding” after the Civil War.

Here, we will take a broader look at how the Supreme Court used the Fourteenth Amendment to extend protections that had originally constrained mainly the federal government to the states, and how the Amendment became the basis for vital individual rights involving racial equality, free speech, and abortion.

“No State Shall”: How Individual Rights Came to Bind the States

The Fourteenth Amendment was one of the Civil War’s most important legacies. After the war, the Reconstruction Congress adopted the Thirteenth, Fourteenth, and Fifteenth Amendments, collectively known as the Reconstruction Amendments. The Thirteenth abolished slavery, the Fifteenth protected the voting rights of Black men, and the Fourteenth sought to redefine how civil rights would be protected.

The Citizenship Clause discussed in earlier episodes is only the first sentence of Section One. The second sentence is our focus here:

No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

The subject of this sentence is “No State shall.” That wording is crucial.

The Bill of Rights, ratified in 1791 as the first ten amendments to the Constitution, originally constrained the federal government. The First Amendment, for example, begins, “Congress shall make no law.” In 1833, the Supreme Court further confirmed in Barron v. Baltimore that the Fifth Amendment’s protection of property did not apply to state governments. In other words, before the Fourteenth Amendment, ordinary citizens generally could not invoke the Bill of Rights against a state. A state could restrict certain civil liberties, and the federal courts ordinarily could not intervene on the strength of the Bill of Rights alone.

The Fourteenth Amendment changed that structure. Its subject was “No State,” not “Congress.” From then on, state legislatures, executive officials, and courts could all face federal review for infringing individual rights. The Amendment nationalized the protection of those rights and empowered federal courts to apply constitutional standards vertically throughout the states.

This is a major reason the Fourteenth Amendment is called a “Second Constitution.” The original Constitution of 1787 primarily addressed how the federal government would be formed and how powers would be divided among its institutions. The Fourteenth Amendment of 1868 answered a different question: what lines may a state government never cross in its treatment of individuals?

Writing a rule into the Constitution, however, is one thing; enforcing it is another. The Supreme Court’s cases show how this “Second Constitution” gradually became effective through litigation.

The Slaughter-House Cases: The Privileges or Immunities Clause Locked Shut

Our first decision is the Slaughter-House Cases, which created the first major obstacle to the implementation of the Fourteenth Amendment.

In 1873, only five years after the Amendment was ratified, the Supreme Court confronted a pivotal dispute. Louisiana had passed a law granting one company a monopoly over the slaughterhouse business in New Orleans. Hundreds of independent butchers sued the state, arguing that the law violated the Fourteenth Amendment’s Privileges or Immunities Clause. They claimed that the freedom to choose one’s occupation was a privilege or immunity of American citizenship that a state could not arbitrarily take away.

On its face, this seemed to be the most direct provision for protecting citizens’ rights:

No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States.

The Supreme Court nevertheless rejected the butchers’ claims by a vote of 5–4. In the majority opinion, Justice Samuel Miller divided citizenship into two levels: citizenship of the United States and citizenship of a state. He reasoned that the Privileges or Immunities Clause protected only a limited set of rights arising from the federal government, the federal Constitution, or the national character of the Union—for example, access to the seat of the federal government and federal protection on the high seas. Everyday rights involving occupation, contract, and property, by contrast, generally remained matters of state citizenship.

The consequences were severe. The Court interpreted a clause that appeared to offer direct protection for fundamental rights almost out of existence. Under the American common-law tradition, Supreme Court precedent binds later cases. After Slaughter-House, an ordinary person challenging a state’s violation of fundamental rights in federal court could almost never rely directly on the Privileges or Immunities Clause.

The Fourteenth Amendment had just built a front door for individual rights. Five years later, the Supreme Court locked it. Later courts wishing to use the Amendment to constrain state governments would have to find another entrance.

Selective Incorporation: Making the Bill of Rights Binding on the States

That new entrance was the Due Process Clause of the Fourteenth Amendment:

No State shall deprive any person of life, liberty, or property, without due process of law.

The most straightforward reading treats this as a procedural rule. A government may lawfully restrict liberty, take property, or even deprive someone of life, but before doing so it must provide appropriate notice, a hearing, and an opportunity to be heard. This is what we now call procedural due process. Its primary concern is not whether the government’s ultimate decision was correct, but whether the process by which it reached that decision was fair.

Once the Slaughter-House Cases had blocked the Privileges or Immunities Clause, however, courts gradually gave the Due Process Clause additional functions. The word “liberty,” in particular, became one of the most important and controversial concepts in American constitutional law.

The rights protections developed from the Due Process Clause broadly followed two paths. The first is selective incorporation; the second is substantive due process. The two concepts are often conflated, but they address different questions.

First, selective incorporation.

To “incorporate” a right is to make a protection in the Bill of Rights—originally binding only on the federal government—applicable to the states through the Fourteenth Amendment. The right must already be expressly stated in the constitutional text. The Court asks whether it is “fundamental to the American scheme of justice” and “deeply rooted in this Nation’s history and tradition.” If so, the Court incorporates it through the Fourteenth Amendment. State and federal governments then face the same standard; there is no diluted “state version” of the right.

In 1925, Gitlow v. New York marked an early step toward incorporating freedom of speech against the states. In 1961, Mapp v. Ohio applied the exclusionary rule to them. In 1963, Gideon v. Wainwright held that indigent defendants charged with felonies have a right to appointed counsel. In 2010, McDonald v. Chicago applied the Second Amendment right to keep and bear arms to the states.

Today, most of the protections in the Bill of Rights apply to state governments through selective incorporation. The process has taken more than a century, extending federal constitutional standards across the country one right at a time.

Substantive Due Process: From Freedom of Contract to Marriage and Abortion

The Due Process Clause also opened a second, bolder, and more controversial path: substantive due process.

As we have seen, the clause provides that no state may deprive any person of life, liberty, or property without due process of law. Life and property refer to relatively concrete interests and leave less room for interpretation. “Liberty,” however, is far more open-ended. To protect rights not expressly named in the Constitution, the Supreme Court began interpreting the concept expansively, placing within it rights such as married couples’ access to contraception, same-sex marriage, and a woman’s decision to have an abortion.

The distinction between selective incorporation and substantive due process is therefore clear. The former extends to the states a right already written into the Constitution. The latter identifies, within the word “liberty,” a new kind of right not expressly enumerated in the constitutional text.

Substantive due process was first applied on a large scale in the economic sphere. In Lochner v. New York (1905), the Supreme Court placed “liberty of contract” under the Fourteenth Amendment’s protection and struck down a state law limiting bakers’ working hours. Over the following decades, the Court repeatedly invoked contractual and property liberty to scrutinize state labor protections and economic regulations. This period, during which the federal courts tended to favor business owners, became known as the “Lochner era.”

The tide began to turn during the New Deal. In West Coast Hotel Co. v. Parrish (1937), the Court held that freedom of contract was not absolute and that government could reasonably regulate economic activity to protect workers and the public interest. Economic substantive due process then gradually declined.

The doctrine next moved into marriage, family life, and personal autonomy. Griswold v. Connecticut (1965) recognized the right of married couples to use contraception. In 2015, Obergefell v. Hodges recognized the right to same-sex marriage.

Its most controversial expansion came in Roe v. Wade (1973). By a vote of 7–2, the Supreme Court held that, within certain limits, a woman’s decision to terminate a pregnancy fell within the liberty protected by the Fourteenth Amendment. The decision affected the lives of two generations of Americans and made substantive due process one of the fiercest battlegrounds in American politics.

Critics argued that the Justices appeared to be interpreting constitutional “liberty” while in fact writing their own value judgments into the Constitution. Supporters responded that if the Constitution could protect only fundamental liberties expressly named in its text and could never develop with the times, people long excluded from political power would never receive constitutional protection.

In 2022, Dobbs v. Jackson Women’s Health Organization overruled Roe. By a 6–3 vote, the Court upheld Mississippi’s abortion restriction. The majority concluded that a right to abortion was not “deeply rooted in this Nation’s history and tradition,” did not qualify as a fundamental right protected by the Fourteenth Amendment, and should be returned to the states for democratic resolution.

Dobbs did not end the debate. On the contrary, it brought a more fundamental question back to the surface: how far should courts go in protecting rights that the Constitution does not name? Is “history and tradition” an objective standard, or is it simply another interpretive method that requires value judgments?

The debate over abortion and substantive due process deserves an episode of its own.

Equal Protection: From “Separate but Equal” to Affirmative Action

After due process comes the final sentence of Section One, the Equal Protection Clause:

No State shall deny to any person within its jurisdiction the equal protection of the laws.

In 1896, Plessy v. Ferguson left a grave stain on this clause. By a vote of 7–1, the Supreme Court upheld Louisiana’s racial segregation policy, reasoning that the state could separate people by race without violating the Constitution so long as it nominally provided equal facilities for each race. This became the infamous doctrine of “separate but equal.”

Justice John Marshall Harlan was the only dissenter. He argued that the Constitution should tolerate no class distinctions among citizens. At the time, however, his view did not prevail.

It was not until Brown v. Board of Education, fifty-eight years later, that the Supreme Court formally overruled “separate but equal” in public education. Chief Justice Warren announced for the Court that separating students solely by race imposed an unequal legal status; separate educational facilities were inherently unequal.

Plessy and Brown applied the same constitutional clause but reached opposite results. This shows that equal protection does not simply require government to treat everyone identically. Government can classify people according to certain criteria and sometimes treat those groups differently. The difficult question is which classifications are reasonable and which create hierarchy and discrimination.

This problem became especially visible in affirmative action. After desegregation, the United States began adopting affirmative-action policies in the 1960s. Some universities considered applicants’ race during admissions to increase minority enrollment. Supporters regarded this as a remedy for historical discrimination; opponents argued that, whatever the purpose, government should never again distinguish among individuals by race.

In Students for Fair Admissions, Inc. v. President and Fellows of Harvard College (2023), the Supreme Court invalidated the universities’ race-conscious admissions programs by a vote of 6–2 in the Harvard case. Chief Justice Roberts wrote for the majority: “Eliminating racial discrimination means eliminating all of it.”

From Plessy to Brown and then to Students for Fair Admissions, the question before the Court changed. It began as whether states could openly impose racial discrimination. Later, it became whether government could favor minority groups in an effort to remedy historical discrimination. The Court moved from permitting segregation, to opposing it, and then to limiting race-conscious affirmative action. Those shifts reflect not only the evolution of legal doctrine but also subtle changes in the political climate.

Four Doorways to Rights: The Fourteenth Amendment’s Evolution

We can now pause and look at Section One of the Fourteenth Amendment as a whole.

It provides four doorways to rights: birthright citizenship, privileges or immunities, due process, and equal protection. These doorways do not stand in isolation. After the Slaughter-House Cases sharply narrowed the Privileges or Immunities Clause, the Court shifted much of its rights protection to the Due Process Clause. Due process and equal protection also frequently work together.

The story of the Fourteenth Amendment, however, has never been written by the Supreme Court alone. Courts define the boundaries of rights in individual cases; Congress can enact implementing legislation; and the appointment of Justices, as well as the ultimate enforcement of decisions, is shaped by political and social forces.

Across more than 150 years, the Amendment has not followed a straight line of uninterrupted expansion. Its center of gravity has shifted in roughly three stages.

The first was a period of contraction. The Slaughter-House Cases drastically narrowed the Privileges or Immunities Clause, while Plessy tolerated racial segregation. Yet even during a period of overall contraction, the clauses did not all move in the same direction. As discussed in an earlier episode, United States v. Wong Kim Ark established birthright citizenship during this era.

The second was a period of expansion. Through selective incorporation, the Supreme Court extended expressly enumerated rights such as freedom of speech and the right to criminal defense counsel to the states. Through Brown, it abolished racial segregation in public schools. Through substantive due process, it protected marriage, family life, and personal autonomy.

The third is the contemporary period of reconsideration. Dobbs ended nationwide constitutional protection for abortion, while Students for Fair Admissions prohibited universities from favoring minority applicants on the basis of race. The Supreme Court is reassessing which rights should receive uniform national protection and which questions should be returned to the states.

This history also shows that the Fourteenth Amendment’s stability depends on several forces working together. Do rights not expressly written in the Constitution fall within the liberty protected by the Amendment’s Due Process Clause? American society will continue to debate these questions.

Conclusion: Where Will the Fourteenth Amendment Go Next?

Several developments will be worth watching.

First, could rights involving same-sex relationships and same-sex marriage be overturned in a future decision? As American society becomes more conservative and debate over same-sex marriage grows, whether the Supreme Court will reinterpret those rights remains to be seen.

Second, does transgender status constitute a sex-based classification, and what level of equal-protection scrutiny should apply? Disputes over transgender identity, medical care, and sports policy have intensified in recent years. The Supreme Court has begun to enter this field. In United States v. Skrmetti (2025), it upheld Tennessee’s restrictions on certain gender-affirming medical treatments for minors. In West Virginia v. B. P. J. (2026), it held that schools may determine eligibility for women’s and girls’ sports based on biological sex. Even so, major questions remain unresolved, including whether transgender status itself is a suspect or quasi-suspect classification and what standard of review should govern other policies.

Third, after Students for Fair Admissions, universities may not directly treat race as an admissions advantage, but they may consider how an applicant has been affected by racial experience. The boundary between race and individual experience remains exceedingly subtle.

The story of the Fourteenth Amendment is therefore far from over. After more than 150 years of case law, it has become part of the foundational architecture of rights protection in the United States. Yet it is not a self-executing catalogue of rights. It is better understood as an institutional language that is continually interpreted, contested, and revised.

It did not provide every answer at once. It merely opened several doors between the individual and the state. Which door can be opened, and how wide, is determined jointly by congressional legislation, social movements, and generations of judicial decisions.

In the American system, the Supreme Court is often called upon to give the final word. But it can never truly determine the direction of history.

Thank you for reading. If you have questions or thoughts about this article, or would like to hear the full story of any of these cases, please leave a comment. See you next time.

Key Cases Discussed

  • 1833 — Barron v. Baltimore: Held that the Bill of Rights generally did not bind state governments.
  • 1873 — The Slaughter-House Cases: Narrowly interpreted the Privileges or Immunities Clause, forcing later courts to rely more heavily on the Due Process Clause.
  • 1896 — Plessy v. Ferguson: Upheld racial segregation under the doctrine of “separate but equal.”
  • 1898 — United States v. Wong Kim Ark: Established a broad rule of jus soli citizenship.
  • 1905 — Lochner v. New York: Struck down a labor law in the name of freedom of contract, becoming the leading example of economic substantive due process.
  • 1925 — Gitlow v. New York: Marked an important early step toward applying freedom of speech to the states.
  • 1937 — West Coast Hotel Co. v. Parrish: Rejected an absolute freedom of contract and signaled the end of the Lochner era.
  • 1954 — Brown v. Board of Education: Overturned racial segregation in public schools and rejected “separate but equal.”
  • 1961 — Mapp v. Ohio: Applied the exclusionary rule to the states.
  • 1963 — Gideon v. Wainwright: Recognized the right of indigent felony defendants to appointed counsel.
  • 1965 — Griswold v. Connecticut: Protected marital privacy and access to contraception.
  • 1973 — Roe v. Wade: Recognized a constitutional right to abortion.
  • 2010 — McDonald v. Chicago: Applied the Second Amendment right to keep and bear arms to the states.
  • 2015 — Obergefell v. Hodges: Recognized the right to same-sex marriage.
  • 2022 — Dobbs v. Jackson Women’s Health Organization: Returned the regulation of abortion to the states.
  • 2023 — Students for Fair Admissions, Inc. v. President and Fellows of Harvard College / University of North Carolina: Severely restricted race-conscious university admissions.
  • 2025 — United States v. Skrmetti: Upheld Tennessee’s restrictions on certain gender-affirming medical treatments for minors under rational-basis review.
  • 2026 — West Virginia v. B. P. J.: Held that schools may determine eligibility for women’s and girls’ sports based on biological sex.
  • 2026 — Trump v. Barbara: Confirmed the citizenship of children born in the United States to parents who are unlawfully or temporarily present.

Key Concepts

  • Procedural due process: When government deprives a person of life, liberty, or property, it must provide notice, a hearing, and an opportunity to be heard appropriate to the interest at stake.
  • Selective incorporation: The process of incorporating fundamental rights expressly stated in the Constitution into the Fourteenth Amendment and thereby applying them to the states.
  • Substantive due process: The doctrine through which courts identify fundamental rights not expressly enumerated in the Constitution within the word “liberty.”
  • Three tiers of equal-protection review: Strict scrutiny applies primarily to classifications based on race and national origin; intermediate scrutiny applies primarily to sex and nonmarital parentage; rational-basis review applies to ordinary economic and social classifications.