But the problem with this position is that it’s hard to identify exactly what property is supposed to do the work of excluding the unborn from the ranks of humans whom it is wrong to kill. If full personhood is somehow rooted in reasoning capacity or self-consciousness, then all manner of adult human beings lack it or lose it at some point or another in their lives. If the capacity for survival and self-direction is essential, then every infant would lack personhood — to say nothing of the premature babies who are unviable without extreme medical interventions but regarded, rightly, as no less human for all that.

At its most rigorous, the organism-but-not-person argument seeks to identify some stage of neurological development that supposedly marks personhood’s arrival — a transition equivalent in reverse to brain death at the end of life. But even setting aside the practical difficulties involved in identifying this point, we draw a legal line at brain death because it’s understood to be irreversible, the moment at which the human organism’s healthy function can never be restored. This is obviously not the case for an embryo on the cusp of higher brain functioning — and if you knew that a brain-dead but otherwise physically healthy person would spontaneously regain consciousness in two weeks, everyone would understand that the caregivers had an obligation to let those processes play out.