Equality is a bedrock American value, yet somehow it feels like we’re not very good at it. From the founding to the present day, we have always talked pretty well about equality while falling well short of the ideal. It’s worth thinking about why that’s so.

On the one hand, a common-sense understanding of equality is straightforward. Ask any third grader, and they’ll tell you that we shouldn’t treat people differently because of the color of their skin or the fact that they speak accented English.

But on the other hand, it’s obvious that American equality is no simple matter: After more than two centuries working to build a more perfect union, our imperfections are glaring.

To think about what equality means for us today, it can be helpful to look to our past. In particular, the period following the Civil War was a crucial inflection point in American self-understanding. Passage of three constitutional amendments in the immediate aftermath of the war sought to establish a more equal post-slavery America. All three amendments are profoundly important (the 13th freed the slaves; the 15th gave black men the vote), but the 14th Amendment has particular resonance.

The history of our interpretation of the 14th Amendment encapsulates important elements of what we as a nation think about equality, and it shows how our views have evolved over time.

For lots of us, mention of the 14th Amendment doesn’t evoke immediate recognition or familiarity. It might be the most important constitutional amendment you’ve never heard of.

To summarize: The 14th Amendment guarantees equal protection of the law for all, and it directs that no person shall be deprived of life, liberty or property without due process. It’s the most litigated part of our Constitution, and it is implicated in momentous Supreme Court cases that have shaped our nation.

For instance, in its infamous 1896 Plessy v. Ferguson ruling, the Court relied on the 14th Amendment to establish the principle of “separate but equal.” The decision went a long way toward creating the discriminatory practices of the Jim Crow South.

Nearly 60 years later, the court cited the 14th Amendment in deciding Brown v. Board of Education, saying that separate is never equal. This was a direct renunciation of the Plessy decision, and a signal moment in the struggle for civil rights.

Jump forward another 60 years to the summer of 2015, when the court ruled in Obergefell v. Hodges that gay couples have a constitutionally protected right to marry. In the arc from Plessy to Obergefell, we get a sense of the changes in our national conception of equality and inclusiveness.

We are still deeply imperfect. But just as it would be a mistake for us to be too easily satisfied with whatever progress we’ve made, so too must we guard against the easy cynicism that insists equality in America is a fraud and progress is illusion. It’s important that we continue to wrestle with questions of equality. Perhaps most of all, it’s essential that as many people as possible join the conversation.

Hayden Anderson is executive director of the Maine Humanities Council. At 5:30 p.m., on June 1, the council and the University of Maine School of Law will present a free public program at the Portland Public Library on the history, legacy and contemporary significance of the 14th Amendment. Throughout 2016, it will continue to offer ways for Mainers to talk with one another about equality and inclusiveness, in commemoration of the 150th anniversary of the passage through Congress of the 14th Amendment. Visit mainehumanities.org for more information.