Political correctness seems to be at the center of more debates lately, if not explicitly then implicitly. So it’s worthwhile to revisit the historical roots of the P.C. debate, to try to see where this latest version might be headed.

First, as to the definition: People differ on what the term means, but I view political correctness as a complex bundle of beliefs and practices, ranging from simple politeness and consideration to censorship and also vilification of those with different opinions. Often it is an attempt to police discourse so as to avoid any possible offense.

As for the debate: There’s no way to measure precisely, but it seems to me that debates over political correctness were prominent in the 1990s, receded for a while, and have returned with a vengeance in the last decade. Criticisms of cultural appropriation, for instance, came hand-in-hand with the anti-globalization protests of the ’90s, yet dwindled until some recent campus incidents.

What caused the P.C. movement to stall after the ’90s? One theory is that it was due to two particular events. First, a Democratic president was impeached for his sexual conduct with an intern. That made the left (at least temporarily) less interested in rooting out and punishing all abuses of power. Second, the attacks of Sept. 11, and the subsequent wars in Afghanistan and Iraq, created a new and different focal point for activist energy: first anti-terror, then anti-war.

The history of political correctness also shows that ideas can have a long genesis, as this essay by Musa al-Gharbi illustrates. The idea of sensitivity training, for instance, was created by Kurt Lewin in 1946-47, and later popularized by Carl Rogers in 1961. The notion of “safe spaces” started in gay and lesbian bars in the mid-1960s. The term “microaggressions” comes from Chester Pierce in 1974. It is possible that the phrase “identity politics” comes from the Combahee River Collective Statement of 1977.

The lesson here is clear: If you are dealing in the world of ideas, play the long game. Don’t be too discouraged by momentary setbacks. For all the talk of America having a throwaway culture that moves rapidly from one idea to the next, the history of political correctness does not support that vision. It is possible for people to promote and sustain ideas to give them resonance and influence.

Another lesson is that the 1960s and ’70s were truly an influential and creative time in U.S. intellectual, political and ideological history. America is still litigating the debates from that time — in contrast to the ideas from the 1980s and ’90s, which stressed the triumph of liberalism, now a somewhat doubtful proposition and not obviously the wave of the future.

In one regard, however, America is rejecting the legacy of the ’60s hippie movement — and for the better. The culture of the ’60s granted considerable latitude to sexually aggressive men. These days the standards for appropriate behavior are much tougher, and rightly so. The P.C. movement gets some of the credit.

The political correctness movement is also notable for its female leadership. Its single most important intellectual force has probably been Catharine MacKinnon, a law professor the University of Michigan and Harvard. She promotes the notion that words can do harm and that free-speech rights are not absolute, and has suggested that pornography should be subject to tougher regulation. Those are not new ideas, but they re-emerged in a new framework and have become more influential.

The treatment of gay Americans emerges as perhaps the greatest success of the political correctness movement. Reading the recent Susan Sontag biography, I was struck not only by her radical thinking but also by how reluctant she was, in the 1990s, to come out as lesbian. That has since changed for the better, and again the P.C. movement is partly to thank.

Also notable is how much the political correctness movement, at least on campus, reflects the power of the so-called middle. Debates over political correctness are not usually looked upon favorably by university presidents or other top administrators, who have the responsibility of raising money and keeping the campus functioning. Nor are they driven by the least successful students, who tend to be disengaged. Instead, it is often mid-level administrators — deans of student affairs, say, or diversity officers — mobilizing a middle and upper tier of students.

Debates over political correctness inspire a lot of passion, and rightly so. Looking past the polemics and considering the history, I am struck by the ebb and flow: Even the most popular ideas and arguments in today’s debate are likely to become less so over time — but no matter how unpopular they become, they will never completely go away. The debates have resulted in a complex web of winners and losers, some very real social gains, and a series of now-escalating excesses. Most of all, however, what they show is that ideas will always matter.

Tyler Cowen is a Bloomberg Opinion columnist. He is a professor of economics at George Mason University and writes for the blog Marginal Revolution. His books include “Big Business: A Love Letter to an American Anti-Hero.”