Soul and Spirit are NOT the same concept
A soul is that which gives life to a living body. A spirit is that which can exist and act without a body. We see by their different definitions that soul and spirit are not necessarily to be equated. The only case where we find a soul which is also a spirit is in that of the human soul.
Soul is the principle of life in a living body. The soul is the substantial form of the body. It gives life, confers the nature, provides order and unity of purpose to the living organism. The soul has no organ and cannot be detected by empirical examination. The soul is the remote efficient cause and radical principle of all the acts of the organism. The activity of each organ and its coordination with the other organs for the good of the whole body cannot be explained without a universal intrinsic principle of life which animates and organizes the organs and which itself is not one of them.
The material soul is called material not because it is made of matter but because it is dependent upon matter for its be and for its do. The material soul is the principle of life of a creature which will cease to exist at death, namely, the plant or the brute animal. While the body depends for its life upon its soul, the material soul depends upon a suitable organization of the body for it to be able to maintain its own existence and its vivifying influence. For the material soul is not created i.e. made out of nothing, but is educed from the potency of the matter and returns to the potency of matter when the body through age or disease or injury is no longer able to support the soul. We do not say that life comes from non-life but that actual life can come from virtual life. For example an apple seed is not actually an apple tree but contains one virtually. If the seed is planted and the right conditions exist then the matter will become sufficiently disposed for the soul to arise and actually (rather than virtually) give life and order to the beginnings of an actual (rather than a virtual) apple tree. The material soul is not a thing in its own right but the principle of a thing. It cannot exist by itself but only as the form of the living body.
The vegetative soul is that which gives life to a plant. It is the lowest soul but not the lowest substantial form. The lowest substantial forms, which are not souls, are those of non-living things. The distance between vegetative life and non-living creation is infinite because it is the difference between be and be-not (and there is no middle between these). The vegetative soul is therefore infinitely superior to the substantial forms of inanimate things (e.g. water, gold, nitrogen). The vegetative soul is the root or radical principle of the plant's powers and acts: nutrition, growth and generation. The vegetative soul is formally one i.e. is one soul and virtually one i.e. has the power of one soul. The vegetative soul is intrinsically dependent on matter and returns to the potency of matter when the body fails.
The sensitive soul is that which gives life to a brute (animal). The sensitive soul is infinitely superior to the vegetative soul because it confers on the animal the ability to know and desire. Animals are knowers and plants are non-knowers - this is the difference between be and be-not, an infinite gulf.
The sensitive soul is the root or radical principle of the animal's powers and acts: vegetative functions, senses and sensations, sense appetites and passions. The sensitive soul is formally one i.e. is one soul and virtually two i.e. has the power of two souls - vegetative and sensitive. For the animal has the perfection of the plant and more. The sensitive soul is intrinsically dependent on matter and returns to the potency of matter when the body of the animal fails.
The human soul is that which gives life to a man. The human soul is both a soul and a spirit, but it is not two things - it is one spiritual soul. Because it is spiritual the human soul is created immediately by God in the body prepared by the parents - it is not educed from the potency of matter. The human soul being spiritual is also immortal and so it lives on after the body dies. The human soul is not only a principle of life, it is also a thing in itself - as a spirit - and can thus exist without the body.
The human soul is infinitely superior to the souls of animals and plants because it is spiritual and immortal and has the properties of intellect and free will. The human soul united with its body is the root or radical principle of all man's acts, habits and powers. Because man is both corporeal and spiritual certain of his powers are organic i.e. belonging to body and soul, and others are inorganic i.e. belonging to the soul alone. The organic powers e.g. nutrition, sight, imagination, irascible appetite etc have organs in the body and fail when the body dies. They are said to remain radically in the separated soul. The inorganic powers, i.e. intellect and will, are spiritual and so have no organ in the body, but continue to exist and operate in the soul when it is separated from the body at death.
The human soul is formally one i.e. is one soul and virtually three i.e. has the power of three, vegetative, sensitive and intellective.
A spirit is what does not depend on matter for its existence. The human soul is a spirit but by nature a spirit which gives life to a body. Hence it is not a spirit in every respect. Being the formal principle of a living body, it is also a soul: the only soul which is also a spirit. But a pure spirit is one which is not a soul.
An angel is a pure spirit. Each angel was created immediately by God at the beginning of time. The angelic powers of intellect and will are far more perfect and powerful than those of man because they are not restricted by limitations of the body. They do not know as we do, but are co-created with a participation of the divine knowledge. As pure spirits the angels have great power over the material universe. The angels are graded in such a way that the second least angel has all the perfection of the least angel and more, the third least angel has all the perfection of the second least and more and so on to the greatest angel who has all the perfection of all other angels and more. The angels are by nature immortal. They are sometimes called "the intelligences" and "separated substances".
The angels were not created in their merely natural state but were created with grace and the supernatural virtues and gifts of the Holy Ghost. Those who chose to love God above all things were immediately rewarded with the Beatific Vision. Those spirits who chose to love themselves above all things lost grace and fell into Hell where they as devils suffer everlasting torment. There are possibly more angels than men. The holy angels are sent by God to help us to Heaven. God permits the fallen angels to tempt us so that we may prove our love of and faithfulness to God.
God is the Supreme Spirit. He is uncreated. He is more than immortal or everlasting. He is eternal - without beginning or end. He is Creator of all things. He conserves creatures in their existence and moves them to their acts. God is infinite in every perfection. There is no change in Him - He can neither increase nor diminish. Yet in God there is infinite activity - a life of infinite knowledge and love. God is Pure Act. There is in Him no potency to be realized nor any perfection which can be lost.
Andrew Nimmo is a lecturer at the Centre for Thomistic Studies, in Sydney, Australia.
This article posted December 2000. It was published in Universitas, No. 8 (2000).
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