Fertilization — the fusion of egg and sperm cell — marks the beginning of a new human personhood. From this moment on, a new entity exists with its own nature, its own genetic identity, and its own substance (cf. Bexten 2017, pp. 195 ff.).
Empirically, fertilization unfolds in two steps: the penetration of the egg cell by the sperm and the syngamy — the fusion of the two pronuclei about 22 hours later. Part of the embryological literature regards syngamy, rather than penetration, as the true initiating event of the new organism, because here for the first time a complete, independently acting diploid genome exists (Sadler, Langman’s Medical Embryology, 15th ed. 2023; O’Rahilly & Müller 2010). This dispute shifts the ontological starting date by at most a few hours — it does not call the basic personal-ontological thesis into question.
In the international convention of the Carnegie stages, the zygote corresponds to Carnegie stage 1 (day 1, totipotency); the subsequent cleavage to Carnegie stage 2 (days 2–3). Cf. the overview in Embryo.
What begins at fertilization is not merely a biological process that at some point acquires “personal quality.” From the very beginning it is the personal life of a someone. The spiritual soul — the vital principle of the human being — in-forms the new organism from the first cell on as its essential form. Thomas Aquinas teaches that the soul is the forma corporis, which makes matter into body and the body into the body-soul unity.
The embryo thus possesses all the marks of the first dimension of personhood. It is real, self-subsistent, unique, and has the active disposition to unfold all the personal capacities of the second and third dimension. Spaemann puts it pointedly: “There are no potential persons.” The distinction between act and potency pertains to the capacities, not to personhood itself.
The attempts to relocate the beginning of personhood to a later point in time — for instance to nidation, brain development, or consciousness — rest on the empirical-functionalist concept of person. This conflates personhood with person-behavior (agere sequitur esse). With personhood, the embryo is endowed with inalienable dignity. The personalist norm holds from the moment of fertilization.
Chapter assignment: Chapter 4: What is human personhood? (esp. 4.7.3), Chapter 5: Oblivion of the Person
Conception
Conception is the completion of gamete fusion, with which the human person begins to exist. It marks the beginning of the first dimension and of the lifespan. Conception is an event — not a process — that sets the ontological starting point of personhood. From this moment on, the person is fully present: not as a “potential person,” but as an actual person with all essential characteristics as a fundamental endowment. Conception initiates the prenatal phase, which is divided into the embryonic and fetal phase.
Ontological classification: Genus: Event, process; marks the beginning of: lifespan, prenatal phase
Birth
Birth is the transition from the prenatal to the postnatal phase of human life. It does not change the ontological status of the person: the human being before birth is the same person as after birth. Dignity and personhood do not begin with birth, but with fertilization. Birth does, however, mark a significant transition: the child emerges from the unique bodily closeness to the mother into the world of interpersonal encounter, of public space, and of familial community. The embryo or unborn child is ontologically already a full person — birth adds nothing to this.
Ontological classification: Genus: Event
Sources: Generated by querying the Personhood ontology.
Further sources:
- Thomas Aquinas: Summa Theologiae I, q. 76, a. 1 (on the soul as forma corporis).
- Spaemann, Robert: Persons: The Difference between ‘Someone’ and ‘Something’. Transl. Oliver O’Donovan. Oxford: Oxford University Press, 2006 (on the principle “There are no potential persons”).
- O’Rahilly, R. & Müller, F. (2010): Developmental Stages in Human Embryos: Revised and New Measurements. Cells Tissues Organs 192(2): 73–84.
- Sadler, T. W. (2023): Langman’s Medical Embryology. 15th ed. Wolters Kluwer.
See also
- Beginning of Human Existence — six steps toward the question of when the human being begins
- Human Person
- Biological Life
- Synthetic Embryo Model (iBlastoid) — distinction: not a person, because no fertilization
- Oblivion of the Person
- Concept of Person
- Basal Relations