3 Allow me, therefore, to bring before you a subject which I beseech you not to refuse to open up and discuss with me. Many are perplexed by questions concerning the soul, and I confess that I myself am of this number. I shall in this letter, in the first place, state explicitly the things regarding the soul which I most assuredly believe, and shall, in the next place, bring forward the things regarding which I am still desirous of explanation.
The soul of man is in a sense proper to itself immortal. It is not absolutely immortal, as God is, of whom it is written that He “alone has immortality,” for Holy Scripture makes mention of deaths to which the soul is liable— as in the saying, “Let the dead bury their dead;” but because when alienated from the life of God it so dies as not wholly to cease from living in its own nature, it is found to be from a certain cause mortal, yet so as to be not without reason called at the same time immortal.
The soul is not a part of God. For if it were, it would be absolutely immutable and incorruptible, in which case it could neither go downward to be worse, nor go onward to be better; nor could it either begin to have anything in itself which it had not before, or cease to have anything which it had within the sphere of its own experience. But how different the actual facts of the case are is a point requiring no evidence from without, it is acknowledged by every one who consults his own consciousness. In vain, moreover, is it pleaded by those who affirm that the soul is a part of God, that the corruption and baseness which we see in the worst of men, and the weakness and blemishes which we see in all men, come to it not from the soul itself, but from the body; for what matters it whence the infirmity originates in that which, if it were indeed immutable, could not, from any quarter whatever, be made infirm? For that which is truly immutable and incorruptible is not liable to mutation or corruption by any influence whatever from without, else the invulnerability which the fable ascribed to the flesh of Achilles would be nothing peculiar to him, but the property of every man, so long as no accident befell him. That which is liable to be changed in any manner, by any cause, or in any part whatever, is therefore not by nature immutable; but it were impiety to think of God as otherwise than truly and supremely immutable: therefore the soul is not a part of God.
4. That the soul is immaterial is a fact of which I avow myself to be fully persuaded, although men of slow understanding are hard to be convinced that it is so. To secure myself, however, from either unnecessarily causing to others or unreasonably bringing upon myself a controversy about an expression, let me say that, since the thing itself is beyond question, it is needless to contend about mere terms. If matter be used as a term denoting everything which in any form has a separate existence, whether it be called an essence, or a substance, or by another name, the soul is material. Again, if you choose to apply the epithet immaterial only to that nature which is supremely immutable and is everywhere present in its entirety, the soul is material, for it is not at all endowed with such qualities. But if matter be used to designate nothing but that which, whether at rest or in motion, has some length, breadth, and height, so that with a greater part of itself it occupies a greater part of space, and with a smaller part a smaller space, and is in every part of it less than the whole, then the soul is not material. For it pervades the whole body which it animates, not by a local distribution of parts, but by a certain vital influence, being at the same moment present in its entirety in all parts of the body, and not less in smaller parts and greater in larger parts, but here with more energy and there with less energy, it is in its entirety present both in the whole body and in every part of it. For even that which the mind perceives in only a part of the body is nevertheless not otherwise perceived than by the whole mind; for when any part of the living flesh is touched by a fine pointed instrument, although the place affected is not only not the whole body, but scarcely discernible in its surface, the contact does not escape the entire mind, and yet the contact is felt not over the whole body, but only at the one point where it takes place. How comes it, then, that what takes place in only a part of the body is immediately known to the whole mind, unless the whole mind is present at that part, and at the same time not deserting all the other parts of the body in order to be present in its entirety at this one? For all the other parts of the body in which no such contact takes place are still living by the soul being present with them. And if a similar contact takes place in the other parts, and the contact occur in both parts simultaneously, it would in both cases alike be known at the same moment, to the whole mind. Now this presence of the mind in all parts of the body at the same moment, so that in every part of the body the whole mind is at the same moment present, would be impossible if it were distributed over these parts in the same way as we see matter distributed in space, occupying less space with a smaller portion of itself, and greater space with a greater portion. If, therefore, mind is to be called material, it is not material in the same sense as earth, water, air, and ether are material. For all things composed of these elements are larger in larger places, or smaller in smaller places, and none of them is in its entirety present at any part of itself, but the dimensions of the material substances are according to the dimensions of the space occupied. Whence it is perceived that the soul, whether it be termed material or immaterial, has a certain nature of its own, created from a substance superior to the elements of this world—a substance which cannot be truly conceived of by any representation of the material images perceived by the bodily senses, but which is apprehended by the understanding and discovered to our consciousness by its living energy. These things I am stating, not with the view of teaching you what you already know, but in order that I may declare explicitly what I hold as indisputably certain concerning the soul, lest any one should think, when I come to state the questions to which I desire answers, that I hold none of the doctrines which we have learned from science or from revelation concerning the soul.
5. I am, moreover, fully persuaded that the soul has fallen into sin, not through the fault of God, nor through any necessity either in the divine nature or in its own, but by its own free will; and that it can be delivered from the body of this death neither by the strength of its own will, as if that were in itself sufficient to achieve this, nor by the death of the body itself, but only by the grace of God through our Lord Jesus Christ; and that there is not one soul in the human family to whose salvation the one Mediator between God and men, the man Christ Jesus, is not absolutely necessary. Every soul, moreover, which may at any age whatsoever depart from this life without the grace of the Mediator and the sacrament of this grace, departs to future punishment, and shall receive again its own body at the last judgment as a partner in punishment. But if the soul after its natural generation, which was derived from Adam, be regenerated in Christ, it belongs to His fellowship, and shall not only have rest after the death of the body, but also receive again its own body as a partner in glory. These are truths concerning the soul which I hold most firmly.
Source: Letters (New Advent)