"For my own part, I remain convinced, as six other Members of this Court 16 years ago were convinced, that the Roe framework, and the viability standard in particular, fairly, sensibly, and effectively functions to safeguard the constitutional liberties of pregnant women while recognizing and accommodating the State's interest in potential human life. The viability line reflects the biological facts and truths of fetal development; it marks that threshold moment prior to which a fetus cannot survive separate from the woman and cannot reasonably and objectively be regarded as a subject of rights or interests distinct from, or paramount to, those of the pregnant woman. At the same time, the viability standard takes account of the undeniable fact that, as the fetus evolves into its postnatal form, and as it loses its dependence on the uterine environment, the State's interest in the fetus' potential human life, and in fostering a regard for human life in general, becomes compelling. As a practical matter, because viability follows "quickening" -- the point at which a woman feels movement in her womb -- and because viability occurs no earlier than 23 weeks gestational age, it establishes an easily applicable standard for regulating abortion while providing a pregnant woman ample time to exercise her fundamental right with her responsible physician to terminate her pregnancy. [Footnote 2/9] Although I have stated previously for a majority of this Court that "[c]onstitutional rights do not always have easily ascertainable boundaries," to seek and establish those boundaries remains the special responsibility of this Court. Thornburgh, 476 U.S. at 476 U. S. 771. In Roe, we discharged that responsibility as logic and science compelled. The plurality today advances not one reasonable argument as to why our judgment in that case was wrong and should be abandoned."