Progressives seem to believe that Judge Ketanji Brown Jackson’s most relevant qualification for the U.S. Supreme Court is not that she is a Harvard-educated lawyer with an impressive resume, but that she is a Black woman. But, ironically, Judge Jackson can’t seem to define what a woman is.

On day two of her confirmation hearing, in response to questioning from Sen. Marsha Blackburn (R-TN), Jackson said that she cannot define the word “woman” because she is “not a biologist.”

Most dictionaries (which, of course, are not written by biologists) define “woman” as “an adult female human being.” This has been the accepted public meaning of the term since anyone can remember. But on Tuesday, Jackson would not commit to this previously uncontroversial notion. This is disturbing for a number of reasons, not the least of which is that, in the law, the written word is supposed to mean what it says.

The question posed by Blackburn did not, as some commentators have suggested, come out of left field. It was a follow-up to another question about the late Justice Ruth Bader Ginsburg’s statement, in U.S. v. Virginia, that men and women are not “fungible” and that physical differences between the sexes “are enduring.” Jackson refused to say whether she agreed with Justice Ginsburg on this elementary point. So, Blackburn probed further: “Can you define ‘woman’?”

“I can’t,” Judge Jackson answered.

Which begs the question: If a judge cannot say what words are commonly understood to mean, how is she to do her job? By reference to modern notions of social justice?