The question of whether a fetus is a person often turns on why killing adult humans or infants is considered wrong in the first place. If the reason is that they are persons, then whatever grounds personhood must apply consistently across all humans we already agree cannot be killed.
Attempts to ground personhood in mental abilities quickly collapse under scrutiny. Simple awareness of the world cannot be the standard, since many animals possess awareness but are not regarded as moral equals to humans. Self-awareness also fails, because newborn infants lack reflective self-awareness, yet killing them is still understood to be gravely wrong.
Another common proposal is sentience, but this standard proves unstable. Humans under anesthesia or in a temporary, reversible coma are not sentient at the moment, yet they do not lose their status as persons. To preserve their personhood, additional conditions are often added—such as having been sentient in the past or being capable of future sentience. At that point, however, sentience itself is no longer doing the explanatory work; the real criterion has shifted to something deeper and more enduring than current mental activity. These added conditions function primarily to exclude unborn humans rather than to explain why persons have value.
A more coherent and consistent grounding for personhood is human nature. On this view, individuals are persons because of what they are—not because of what they can currently do. If human nature is sufficient to ground the personhood of adults, infants, and temporarily unconscious individuals, then unborn humans, who share that same nature, are persons as well. Excluding them requires an arbitrary line that cannot be defended without undermining the personhood of other vulnerable humans.
Key Takeaways
Ability-based definitions of personhood are inconsistent, since they would exclude infants, the unconscious, and the temporarily incapacitated.
Sentience cannot ground personhood, because humans retain their right to life even when they are not sentient.
Ad hoc additions to sentience standards reveal bias, functioning mainly to exclude unborn humans rather than explain human value.
Human nature provides a stable, equal basis for personhood, and unborn humans share that same nature, making them persons deserving protection.