CHAPTER LVIII—That Vegetative, Sentient, and Intelligent are not in man Three Souls

PLATO lays it down that not one and the same soul is in us at once intelligent, sentient, and vegetative.³²⁷³²⁷From his references, St Thomas appears to have been more familiar with the Timaeus than with any other of Plato’s writings. That poetic, mystical and obscure dialogue was a special favourite of the Neoplatonists, from whom St Thomas gathered his knowledge of Plato. The passage, Timaeus, 69c-70a describing how “the mortal kind of soul,” with its two divisions, was allocated in the body by inferior deities, after the Supreme Deity had produced the intellect, misled early commentators, and after them St Thomas, into the belief that Plato supposed three distinct souls in one human body. Plato never speaks of ‘souls’ except in reference to distinct bodies. He speaks of ‘the soul’ of man as familiarly as we do. The νοῦς in the head, the θυοός (St Thomas’s pars irascibilis) in the chest, and the ἐπιθυμίαι (pars concupiscibilis) in the belly, are not three souls, but three varieties of one soul. Cf. Timaeus, 89e, “three kinds of soul have been put to dwell in us in three several places: Tim. 79 d, “what the soul has of mortal and of divine in its being”: Republic, 439e, “two kinds being in the soul”: Rep. 441 c, “there are varieties in the soul of each individual.” In Laws, 863b he doubts whether the θυμός is to be called “an affection or a part of the soul.” In the ultimate analysis of Plato’s meaning nothing more will appear, I believe, than the triple division, accepted by Aristotle and St Thomas, of νοῦς, θυμός, ἐπιθυμία, three phases of one soul, the first inorganic and spiritual, the two latter organic and involving connexion with the body. In this view, granted that the sentient soul is the form of the body, it does not follow that any subsistent intelligence can be the form of a body. The untenableness of this position is thus to be shown.

1. Attributes of the same subject representing different forms are predicated of one another accidentally: thus ‘white’ is said to be ‘musical’ accidentally, inasmuch as whiteness and music happen both to be in Socrates. If then the intelligent, sentient, and vegetative soul are different powers or forms in us, then the attributes that we have according to these forms will be predicated of one another accidentally. But according to the intelligent soul we are called ‘men,’ according to the sentient ‘animals,’ according to the vegetative ‘living.’ This then will be an accidental predication, ‘man is an animal,’ or ‘an animal is a living creature.’ But on the contrary these are cases of essential predication: for man, as man, is an animal; and an animal, 121as an animal, is a living creature. Therefore it is from the same principle that one is man, animal, and alive.³²⁸³²⁸In a paragraph here omitted occur these words, which are of interest in the discussion of evolution. “The order of the sentient to the intelligent, and of the vegetative to the sentient, is as the order of potentiality to actuality: for the intelligent is posterior in generation to the sentient, and the sentient to the vegetative: for animal is prior in generation to man.” St Thomas is here describing the development of the individual, as Chap. LXXXVI shows, not of the race; or what is now called ‘ontogenetic’ as opposed to ‘phylogenetic’ development.

2. A thing has unity from the same principle whence it has being, for unity is consequent upon being. Since then everything has being from its form, it will have unity also from its form. If therefore there are posited in man several souls, as so many forms, man will not be one being but several. Nor will the order of the forms to one another, one ensuing upon the other, suffice for the unity of man: for unity in point of orderly succession is not absolute unity: such unity of order in fact is the loosest of unities.³²⁹³²⁹e.g., the unity of a dynasty of kings, or of a line of bishops, now called ‘continuity.’

4. If man, as Plato held, is not a compound of soul and body, but is a soul using a body; either this is understood of the intelligent soul, or of the three souls, if there are three, or of two of them. If of three, or two, it follows that man is not one, but two, or three: for he is three souls, or at least two. But if this is understood of the intelligent soul alone, so that the sentient soul is to be taken for the form of the body, and the intelligent soul, using the animate and sentient body, is to be man, there will still ensue awkward consequences, to wit, that man is not an animal, but uses an animal; and that man does not feel, but uses a thing that does feel.

5. Of two or three there cannot be made one without anything to unite them, unless one of them stands to the other as actuality to potentiality: for so of matter and form there is made one without any external bond to bind them together. But if in man there are several souls, they do not stand to one another as matter and form, but they are all supposed to be actualities and principles of action. If then they are to be united to make one man, or one animal, there must be something to unite them. This cannot be the body, since rather the body is made one by the soul: the proof of which fact is that, when the soul departs, the body breaks up. It must be some more formal principle that makes of those several entities one; and this will be rather the soul than those several entities which are united by it. If this again has several parts, and is not one in itself, there must further be something to unite those parts. As we cannot proceed to infinity, we must come to something which is in itself one; and this of all things is the soul.³³⁰³³⁰This argument is from Aristotle, De anima, I, v, nn. 26-28. There must therefore in one man, or one animal, be one only soul.