The human embryo is a person from the very beginning — from the fusion of the germ cells onward. It is not a possible person, not a person-in-the-making, not a “potential person.” It is an actual, complete person who will unfold. It has everything required to be a person, for personhood does not hinge on the unfolding of capacities but on being itself (cf. Bexten 2017, pp. 155—175, 183—202).
The distinction between act and potency is decisive here: the embryo does not merely have the passive possibility of one day thinking (as a block of marble has the passive possibility of becoming a statue). It has the active disposition toward it — it strives from within toward the unfolding of its capacities for thought, will, and love. No physician must tell the embryo how to form a brain; no engineer must show it how to build a heart. All of this happens from within, by virtue of its own spiritual principle of life — the spiritual soul, which informs its whole body from the very first cell.
The embryo lives in the first dimension of personhood: the foundational spiritual existence that does not yet presuppose actual consciousness. It possesses the inalienable dignity that belongs to every someone. The division between “merely biological” and “properly personal” life is artificial: its biological life is, from the first second, the life of a person. Spaemann formulates it thus: “There are no potential persons.” Josef Seifert and Karol Wojtyła share this position, which is directed against the empirical-functionalist concept of person (Singer, Locke).
Arguments That Sustain the Personhood of the Embryo
The personhood of the embryo does not follow from a single observation but from the interplay of several arguments:
- Beginning of Human Existence — six steps to the question of when the human being begins; it bundles the ontological and normative line.
- *Potentiality Argument — active potency rather than mere possibility; the embryo is already a person, because rational nature unfolds, it is not first acquired (Pöltner, Spaemann).
- Nature as Ground — rational nature is the ontological ground of personhood, not the actual performance; agere sequitur esse.
- Exclusion Objection — whoever ties personhood to actual capacities necessarily excludes embryos, the sleeping, and the demented from the circle of persons — a consequence that refutes the position itself.
- Diachronic Identity Objection — psychological continuity cannot explain the identity of the embryo with the later adult; only a substantial bearer can explain it.
- Performative Contradiction — whoever denies the embryo personhood always already presupposes, in the act of arguing, the personhood he theoretically denies.
- Substance-Ontological Concept of Person — the framework in which the above arguments converge (Boëthius, Aquinas, Spaemann).
Course of Development — Carnegie Stages (CS 1–23)
The international standardization of human embryonic development follows the 23 Carnegie stages (O’Rahilly & Müller, Cells Tissues Organs 192:73–84, 2010). They order the embryo not by days in the womb but by morphologically defined steps — this is the only internationally comparable frame of reference. For the argument of personal ontology, the following landmarks are especially relevant:
- CS 1 (day 1) — zygote after syngamy. Beginning of the new organism. Totipotency.
- CS 2 (days 2–3) — cleavage, morula (2–16 cells). Totipotency of the early blastomeres.
- CS 3 (days 4–5) — free blastocyst; first lineage differentiation into inner cell mass (ICM, source of naive pluripotency) and trophoblast.
- CS 4–5 (days 6–12) — implantation; bilaminar germ disc; primed pluripotency in the epiblast.
- CS 6–7 (days 17–19) — primitive streak; beginning of gastrulation. End of the possibility of monozygotic twinning. Classical boundary of the ISSCR 14-day rule.
- CS 8–12 (days 23–30) — neurulation; closure of the rostral and caudal neuropore.
- CS 10 (day 28) — first heartbeat; pharyngeal arches 1–2.
- CS 13–23 (days 32–56) — organogenesis; by the end all organ primordia are laid down.
- From week 9 onward — transition into the fetal phase: growth and maturation of the structures already laid down.
This developmental logic changes nothing in the finding of personal ontology — from CS 1 onward a person is present in the first dimension. The Carnegie stages describe how this person unfolds, not whether and when it comes to be.
The pluripotency hierarchy (toti- → naive pluri- → primed pluri- → multi- → unipotent) is codified in the ISSCR Standards for Human Stem Cell Use in Research (2023). It is a statement about the differentiation latitudes of cells, not about the personhood of the organism to which they belong.
At the cellular level, the HuDeCA cell atlases have, since 2019, mapped embryonic development at single-cell resolution for the first time (Tyser/Srinivas 2021 for CS 7; Cao 2020, Suo 2022, Braun 2023 for the subsequent stages). The atlases supplement the morphological Carnegie convention with a cellular layer — they show cell-fate decisions as gradual and multimodal, which empirically supports the substance-ontological thesis of the person’s beginning at the integral organism at CS 1.
Ontological classification: Superordinate term: Prenatal phase (as embryonic phase)
Chapter assignment: Chapter 4: What is human personhood? (esp. 4.4.3, 4.6.5, 4.7.3), Chapter 1
Sources: Generated by querying the Personhood ontology.
Further sources:
- Spaemann, Robert: Persons. The Difference between “Someone” and “Something”. Translated by Oliver O’Donovan. Oxford: Oxford University Press, 2006 (“There are no potential persons”).
- Pöltner, Günther (2005): Ontologische Voraussetzungen der Debatte über den Embryonenschutz. In: Nowotny / Staudigl (eds.), Perspektiven des Lebensbegriffs. Randgänge der Phänomenologie (Europaea memoria I/34), Georg Olms, Hildesheim. (German)
- Pöltner, Günther (2015): Menschennatur und Speziesismus. In: Rothhaar, Markus & Hähnel, Martin (eds.): Normativität des Lebens – Normativität der Vernunft?. Berlin/Munich/Boston: De Gruyter, pp. 251–270. (Rejection of the speciesism objection against the substance-ontological concept of person.) (German)
- O’Rahilly, R. & Müller, F. (2010): Developmental Stages in Human Embryos: Revised and New Measurements. Cells Tissues Organs 192(2): 73–84. (Standard reference for the Carnegie-stage convention.)
- ISSCR (2023): Standards for Human Stem Cell Use in Research. International Society for Stem Cell Research. (Codifies the toti-/naive pluri-/primed pluri-/multi-/unipotency hierarchy.)
- Tyser, R. C. V.; Mahammadov, E.; Nakanoh, S.; Vallier, L.; Scialdone, A. & Srinivas, S. (2021): Single-cell transcriptomic characterization of a gastrulating human embryo. Nature 600(7888): 285–289. (HuDeCA, CS 7.)
- Cao, J.; O’Day, D. R.; Pliner, H. A.; … & Shendure, J. (2020): A human cell atlas of fetal gene expression. Science 370(6518): eaba7721. (HuDeCA, ~4 million cells, 15 organs.)
- Suo, C.; Dann, E.; Goh, I.; … Haniffa, M.; Teichmann, S. A. et al. (2022): Mapping the developing human immune system across organs. Science 376(6597): eabo0510.
- Braun, E.; Danan-Leon, M.; Hochgerner, H.; … & Linnarsson, S. (2023): Comprehensive cell atlas of the first-trimester developing human brain. Science 382(6667): eadf1226.
See also
- Beginning of Human Existence — six steps to the question of when the human being begins
- Potentiality Argument — active potency, prote/deutera energeia
- Fertilization — fusion of the germ cells as the ontological starting point
- Supernumerary Embryo — IVF follow-on problem
- Embryo Transfer
- Frozen Embryo Transfer (cryotransfer)
- Embryo Donation
- Embryo Research Use
- Indefinite Cryostorage
- Synthetic Embryo Model (iBlastoid) — demarcation
- Exclusion Objection
- Diachronic Identity Objection
- Performative Contradiction
- Nature as Ground
- Empirical-Functionalist Concept of Person (the criticized counter-position)
- Substance-Ontological Concept of Person
- Personalist Norm
- Abortion — normative consequence
- Preimplantation Genetic Diagnosis
- Artificial Fertilization
- Chapter 5: Oblivion of the Person
- Human Person
- Right to Life
- Ontological Dignity
- Second Dimension
- Third Dimension
- Body-Soul Unity
- Argument Map of the Concept of Person