Opinion of the Court
the ground that it creates an “undue burden” because the burden it imposes, though slight, outweighs its negligible benefits? Casey does not say, and this ambiguity would lead to confusion down the line. Compare June Medical, 591 U. S., at ___–___ (plurality opinion) (slip op., at 1–2), with id., at ___–___ (Roberts, C. J., concurring) (slip op., at 5–6).
The third rule complicates the picture even more. Under that rule, “[u]nnecessary health regulations that have the purpose or effect of presenting a substantial obstacle to a woman seeking an abortion impose an undue burden on the right.” Casey, 505 U. S., at 878 (emphasis added). This rule contains no fewer than three vague terms. It includes the two already discussed—“undue burden” and “substantial obstacle”—even though they are inconsistent. And it adds a third ambiguous term when it refers to “unnecessary health regulations.” The term “necessary” has a range of meanings—from “essential” to merely “useful.” See Black’s Law Dictionary 928 (5th ed. 1979); American Heritage Dictionary of the English Language 877 (1971). Casey did not explain the sense in which the term is used in this rule.
In addition to these problems, one more applies to all three rules. They all call on courts to examine a law’s effect on women, but a regulation may have a very different impact on different women for a variety of reasons, including their places of residence, financial resources, family situations, work and personal obligations, knowledge about fetal development and abortion, psychological and emotional disposition and condition, and the firmness of their desire to obtain abortions. In order to determine whether a regulation presents a substantial obstacle to women, a court needs to know which set of women it should have in mind and how many of the women in this set must find that an obstacle is “substantial.”
Casey provided no clear answer to these questions. It said that a regulation is unconstitutional if it imposes a
