THE showdown between the Justice Department and North Carolina officials over a new state law restricting bathroom access for transgender people has brought a question into sharp relief: Does Title VII of the Civil Rights Act of 1964, which bars discrimination because of sex, also prohibit discrimination because of gender identity?

The Obama administration thinks so, as do several district and circuit courts. But North Carolina officials call that a “baseless and blatant overreach” and a “radical reinterpretation” of Title VII. They argue that the authors of the law did not have transgender people in mind when they wrote it.

But that position not only misunderstands how legislative interpretation works, it also fails to grasp the historic complexities of Title VII’s sex provision. The provision has always been contested. Since we don’t know much about why Congress enacted it, we have to look at how courts have interpreted it over the years — and they have constantly expanded its meaning.

In the original bill, Title VII prohibited on-the-job discrimination only on the basis of race, color, national origin and religion. But shortly before it passed the House, Representative Howard Smith of Virginia added “sex” — perhaps as a poison pill, or to protect white women as well as black women. In any case, because the amendment was made during floor debate, we have almost no record of what representatives were thinking when they voted on it.