What is different about a fetus at this later stage to deserve a rational soul?

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    A's often cited discussion about the formation of foetus is Historia Anumalium, book VII, part III but it seems to me that there is no discussion about soul there. Dec 5, 2022 at 11:01
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    Adding sources for the alleged claims would help.
    – Philip Klöcking
    Dec 5, 2022 at 11:48
  • See the relevant passage Generation of Animals II.3.736a30-736b3: "concerning the soul in virtue of which an animal is so called (and this is in virtue of the sensitive part of the soul)—does this exist originally in the semen and in the embryo or not, and if it does whence does it come? For nobody would put down the embryo as soulless or in every sense bereft of life (since both the semen and the embryo of an animal have every bit as much life as a plant), and it is productive up to a certain point. Dec 5, 2022 at 15:43
  • That then they possess the nutritive soul is plain (and plain is it from the discussions elsewhere about soul why this soul must be acquired first). As they develop they also acquire the sensitive soul in virtue of which an animal is an animal, . . . For e.g. an animal does not become at the same time an animal and a man or a horse or any other particular animal. For the end is developed last, and the peculiar character of the species is the end of the generation in each individual. Dec 5, 2022 at 15:44
  • Hence arises a question of the greatest difficulty,which we must strive to solve to the best of our ability and as far as possible. When and how and whence is a share in reason acquired by those animals that participate in this principle? It is plain that the semen and the embryo, while not yet separate, must be assumed to have the nutritive soul potentially, but not actually. And it is clear that we must be guided by this in speaking of the sensitive and the rational soul. For all three kinds of soul,not only the nutritive, must be possessed potentially before they are possessed in actuality. Dec 5, 2022 at 15:46

3 Answers 3


Aristotle believed in a tripartite soul, with 'vegetable' souls and animal souls, supporting only in humans, the intellective soul.

So you would have to think a baby had not begun to have an intellective soul until some stage of development. For Greeks pneuma, breath, was often regarded as spiritual. Children could have survived at several months premature. I would expect some kind of link there. But I don't think the explicit derails are there in their texts.

See this similar discussion for direct quotes of relevance: Did Aristotle believe in an immortal soul?

  • But where A discuss the "moment" where the soul enter the foetus? Dec 5, 2022 at 13:56

Historically speaking, most cultures held that a child becomes 'alive' at the quickening of the fetus — when the woman can begin to feel the fetus move within her — which occurs roughly halfway through pregnancy. Religions that posit a soul usually placed its entry at that time. This is (interestingly) why most abortion laws limit abortions to the first trimester; they are trying to respect religious sentiments.

The idea that the soul enters the body at conception is a recent phenomenon, developed within US Christian fundamentalist and evangelical churches to oppose permissive abortion policies that followed Roe v Wade. It has no real historical or biblical roots, but is a typically hyperbolic assertion made for political advantage. That's not trying to suggest that it's right or wrong, merely that it is motivated by something other than scientific or philosophical reasoning.

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    Who has argued against abortion based on when the soul enters the body? I don't think I've ever heard that argument. Dec 6, 2022 at 6:00
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    The arguments I've seen are based on the claim that after conception, the fetus is a unique and distinct human life. Also, I don't know why you picked out evangelicals as sources of this belief when the Catholics are more radical, disallowing even birth control. Dec 6, 2022 at 7:00
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    @TedWrigley, you have entirely misunderstood the argument. The argument is not that the fetus should not be killed because it is a unique life but because it is a unique human life. There is nothing pseudo-scientific about it. Dec 7, 2022 at 15:18
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    @DavidGudeman: No, I'm not. To say that something is a unique human life merely because it has the correct number and kind of genes would mean that every single cell in one's body is a unique human life, so that we would be committing mass murder every time we cut ourselves, drank a beer, sneezed, or otherwise damaged tissues. Humanity is not determined by mere genetics; the human soul is not a quality of flesh and bone. Dec 7, 2022 at 19:44
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    @TedWrigley, the fertilized egg cell, if all goes right, will develop into a human being. This fact reasonably justifies the claim that the cell is a unique human life, and there is no scientific fact that opposes this assertion. Your use of "pseudo-scientific" in this context is purely political rhetoric, not philosophy (or science). Dec 9, 2022 at 4:08

"Delayed hominization" is a particular case of the larger problem plurality of forms vs. the unity of substantial form:

Ariew, Descartes among the Scholastics (Leiden; Boston: Brill, 2011), pp. 83-84:

  • St. Thomas Aquinas: Man is a unity of single form (the rational soul).5
  • Duns Scotus: Man is a composite of a plurality of forms (rational, sensitive, and vegetative souls)6

  1. Aquinas Summa Theologica, I, quaest. 76, art. 3.
  2. Scotus Opera Omnia, Opus Oxoniense, IV, dist. 11, quaest. 3.

Ariew, Descartes and the Last Scholastics p. 21 fn. 28:

the Augustinian and Franciscan doctrine [was] the plurality of substantial forms. John Duns Scotus and William of Ockham held the thesis that man is a composite of forms (rational, sensitive, etc.), a thesis previously rejected by Thomas Aquinas, who argued that there is just one form or soul in man (the rational soul), which performs the functions that the other souls perform in lower beings.

St. Thomas Aquinas, Summa Theologica I q. 76 a. 3 co.:

an animal would not be absolutely one, in which there were several souls. For nothing is absolutely one except by one form, by which a thing has existence: because a thing has from the same source both existence and unity; and therefore things which are denominated by various forms are not absolutely one; as, for instance, "a white man." If, therefore, man were 'living' by one form, the vegetative soul, and 'animal' by another form, the sensitive soul, and "man" by another form, the intellectual soul, it would follow that man is not absolutely one.

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