In those five words, Justice Thomas punctured Justice Breyer’s 69-page (not including appendices) dissenting opinion in Parents v. Seattle School District No. 1, the Seattle/Louisville cases decided on Thursday. The sentence stands alone in one place and is more fully spelled out in another: “Racial imbalance is not segregation, and the mere incantation of terms like resegregation and remediation cannot make up the difference.”

Thomas’ 36-page opinion is worth reading in its entirety, but this formulation goes to the heart of how cultural Left construes contemporary America. Segregation, Thomas points out, used to “the deliberate operation of a school system” to separate pupils by race. It meant de jure segregation and an active effort by public officials to sort students by race. Justice Breyer, realizing that real segregation is long gone in America’s schools, would nonetheless like to keep the word alive to describe what happens when the racial profile of students attending a school doesn’t match the proportions of races in the larger community.

It is not at all clear that the resulting “racial imbalances” are a social or an educational problem. If they are, it is a paltry one compared to the other manifest defects of our public schools. Calling such racial imbalances “resegregation” is, as Thomas writes, a kind of “incantation.” Breyer would like to invoke the moral authority that comes from opposing racial injustice—even when there is no racial injustice to be found. The Left will almost certainly follow suit. The New York Times already has. “Resegregationist” will be used as this season’s word of opprobrium against anyone who opposes racial preferences in schools or college.