"The good of the grace of one soul is greater than the good of the nature of the whole universe"
- St Thomas Aquinas Ia IIa, q.24, a. 3, ad 2
|REALITY—A Synthesis Of Thomistic Thought
by Reginald Garrigou-Lagrange, O. P.
CH30: THE SEPARATED SOUL 
We treat this subject briefly under three headings:
1. Subsistence of the separated soul.
2. Knowledge of the separated soul.
3. The will of the separated soul.
The continued subsistence of the separated soul may be thus demonstrated. Every form which, in its being, in its specific activity, and in its production, is intrinsically independent of matter, can subsist, and in fact, does subsist, independently of matter. But the human soul is such a form, intrinsically independent of matter. Hence, after the dissolution of the human body, the human soul continues to subsist.
The Averroistic question was this: How can the soul, separated from the matter which gave it individuality, remain individualized, that is, remain as the soul of Peter rather than the soul of Paul? It remains individualized, answers St. Thomas, by its essential, transcendental relation to that human body which originally gave it individuation, even though that body is now buried in the dust. Were this relation merely accidental, then it would disappear with the disappearance of its terminus, as does, e. g.: the relation of a father's paternity when his son dies. But the separated soul is individualized by its relation to an individual body, a relation comparable to that between the soul and the living body, and this relation remains in the separated soul, which by that relation remains individualized. Thus St. Thomas against the Averroists, who, holding that the soul is individualized only by actual union with matter, went on to say pantheistically that all men together have but one immortal and impersonal soul. .
We must note that soul and body form a natural composite, which is one, not per accidens, but per se. Were the human soul united only accidentally to the body, then it would have only an accidental relation to its body, which relation could not remain after the dissolution of the body. Quite otherwise is the case if the human soul is by nature the form of the body.
Here we may again see how faithful St. Thomas is to the principle of economy, which he himself thus formulates:  When fewer principles suffice, search not for more. In the present treatise too he draws all conclusions from principles, very profound but very few. The saint is thus responsible for great progress in the unification of theological knowledge.
Let us note briefly a few more of these consequences. First, it is more perfect for the human soul to be united to the body than to be separated, because its connatural object lies in the sense objects to know which it needs the sense faculties.  Second, the separated soul has a natural desire to be reunited to its body, a conclusion in harmony with the dogma of universal corporeal resurrection.  Third, the separated soul cannot by its will be reunited to its body, because it informs the body, not by its voluntary operation, but by its very nature. .
2. Knowledge 
Sense operations and sense habits do not remain actually in the separated soul, but only radically (i. e.: in their root and principle). What it does actually retain are, first, its immaterial faculties (intellect and will): second, the habits it acquired on earth, habits of knowledge, for example, and third, the actual exercise of these habits, that of reason, for example. Yet the separated soul finds itself impeded in this exercise, because it no longer has the actual cooperation of the imagination and the sense memory. But it receives from God infused ideas comparable to those of the angels. To illustrate, we may compare its state to that of a theologian who, unable to keep in touch with new publications in his science, receives illuminations from on high.
Sometimes we find an emphasis on this last point, an emphasis which neglects another truth, very certain and very important, namely, that the separated soul knows itself directly, without medium.  This truth carries with it many other truths. By this immediate self-knowledge, it sees with perfect evidence its own native spirituality, its immortality, its freedom. It sees also that God is the author of its nature. It thus knows God, no longer in the sense world as mirror, but as mirrored in its own spiritual essence. Hence it sees with transcendent evidence the solution of the great philosophic problems, and the absurdity of materialism, determinism, and pantheism. Further, separated souls have knowledge of one another and also of the angels, though their knowledge of the latter is less perfect, since the angels belong by nature to a higher order of things.
Does the separated soul know what is happening on earth? Not in the natural order. But in the supernatural order, God manifests to the blessed in heaven such events on earth as have a special relation to their blessed state, as, for instance, the question of sanctification of living persons for whom the blessed are praying. .
3. The Will
Every separated soul, so faith teaches us, has a will immutably fixed in relation to its last end. For this truth St. Thomas gives a profound reason. The soul, in whatever state, he says, thinks of its last end rightly or wrongly according to its interior disposition. Now as long as the soul is united to the body, this disposition can change. But when the soul is separated, since it is no longer tending to its last end, it is no longer on the road (in via) to its good, but has obtained its goal, unless it has missed it eternally. Hence its dispositions at the moment of separation remain immovably fixed either in good or in evil.  Here again we see the harmony between dogma and reason, between revelation on the immutability of the separated soul and the doctrine that the soul is the form of the body.
Concluding, St. Thomas,  shows that man, first by his intellectual nature, secondly by grace, thirdly by the light of glory, is made to the image of God. Is man also an image of the Trinity? Yes, by his soul, which is the principle from which proceed both thought and then love.