The Potentiality Argument is the central personal-ontological grounding for why the human embryo is due full personal dignity from conception onward: not because it will one day be a person, but because it is already now the bearer of a rational nature whose powers unfold rather than being first acquired.
The basic idea
In its classical form the argument runs: the embryo will — given intact conditions of development — develop into an adult, rationally acting human being. What develops into something must, in a certain way, already be that into which it develops; development is not production out of nothing, but the unfolding of what is already laid down in active potency. Therefore the embryo is already now a person and must be respected as such.
Precision through act and potency
The decisive differentiation is owed to the Aristotelian-Thomistic doctrine of act and potency, as sharpened in its application to embryo ethics by Günther Pöltner.
Passive potency is mere possibility of being determined by something external — as a block of marble carries within itself the possibility of being formed into a statue by a sculptor. The statue is not in the marble; it must be added.
Active potency, by contrast, is an inner power of self-unfolding — as the acorn actively carries within itself the potency for the oak, is not made into an oak from without, but unfolds into one under suitable conditions.
The potentiality of the embryo is active potency: it is the self-unfolding of an already-present substance of rational nature — not the possibility of first being made into one.
The Spaemann formula
Robert Spaemann’s pointed formulation — “There are no potential persons” — condenses this insight: whoever carries within themselves an active potency toward rationality, self-determination, and self-transcendence is already a person. A “becoming person” in the sense of a not-yet-person that only becomes a person through gradual development does not exist ontologically. There is only a person in becoming — an already-existing person whose rational nature unfolds.
Prote energeia and deutera energeia
The distinction between first and second actuality (prote and deutera energeia) deepens the argument:
- The rational nature — personhood itself — is prote energeia, first actuality. It is fully present from conception onward.
- The actual exercise of rational faculties (speaking, judging, choosing) is deutera energeia, second actuality — the unfolding of what is already actual.
What is still outstanding in the embryo is not the acquisition of the first actuality, but the unfolding of the second. Agere sequitur esse: the rational nature is the presupposition of all rational acts, not their result.
Demarcation against the empirical-functionalist objection
Critics of the argument — prominently Peter Singer and John Locke — demand for personal status the actual exercise of rational faculties. The potentiality argument refutes this empirical-functionalist concept of person on the ontological level: whoever binds personhood to actual acts confuses act and potency; they can no longer explain the unity of the person across sleep, unconsciousness, and developmental phases.
Ontological classification
Superordinate concept: Argument
Supports: Substance-Ontological Concept of Person, right to life of the embryo
Is directed against: Empirical-Functionalist Concept of Person
Presuppositions: act and potency, active potency, Nature as Ground
Chapter assignment: Three Dimensions of Human Personhood (German)
See also
- Embryo
- Beginning of Human Existence
- Act and Potency
- Nature as Ground
- Substance-Ontological Concept of Person
- Right to Life
- Günther Pöltner
- Robert Spaemann
- Thomas Aquinas
- Aristotle
Sources: Generated by querying the Personhood ontology.
Further sources:
- Pöltner, Günther (2005): Der moralische Status des menschlichen Embryos. Imago Hominis 12(2): 109—115.
- Pöltner, Günther (2006): Grundkurs Medizin-Ethik. Wien: Facultas.
- Spaemann, Robert (1996): Personen. Versuche über den Unterschied zwischen etwas und jemand. Stuttgart: Klett-Cotta.
- Spaemann, Robert (1987): “Sind alle Menschen Personen?” In: Grenzen. Zur ethischen Dimension des Handelns. Stuttgart: Klett-Cotta 2001.
- Thomas Aquinas: Summa Theologiae I, q. 76 a. 3; Quaestiones disputatae de anima a. 11.