Reincarnation exerts a real force of seduction on Western mentalities. After a general presentation in the first article, the second article gave the judgments of the Church. The third and fourth sections presented the points of conflict between metempsychosis and Catholic dogma. Subsequent articles examine the question from the point of view of philosophy.
Let us summarize the previously acquired results:
- The soul is the life principle of the body, so it is in a necessary relationship with a body. Contrary to the reincarnation thesis, the living is not the soul alone, but the soul-body combination.
- The soul is the form of the body. The soul therefore gives the body its essence. A human soul cannot communicate vegetable nature to a body.
Therefore, careful analysis of the nature of the soul in itself disproves the thesis of reincarnation. The study of the powers of the soul confirms this result. We will limit ourselves here to the powers that have most to do with our subject: intelligence and memory.
Philosophers oscillate between two contradictory conceptions of human intelligence. Some would like to reduce it to a biological phenomenon. What is called the mind is only the exercise of a developed brain or the imagination. This is the sensualist tendency.
On the contrary, for others human intelligence would be a pure fallen spirit. They then give it either the structure of divine intelligence which itself creates its object, or that of the angels who receive their knowledge by illuminations from above. This is the idealistic tendency. This last current is at the source of the contemporary version of the thesis of reincarnation.
Since human intelligence is born, we are told, to be in direct relation with the spirit world, its sojourn in the body is unnatural. It veils the gaze of the soul and obscures the intelligence. The union of soul and body is therefore detrimental to the soul, which finds itself paralyzed by its fall.
St. Thomas Aquinas responds to this view in an article of singular beauty, in which both the good sense and the wisdom of the doctor shine. 
Let us first clarify a question of method: as we said above, the body is for the soul. The soul determines and constructs the body. So to know whether the union of the human soul to the body is good, or, on the contrary, if it is harmful to the soul, it is necessary to analyze the structure of the soul, and, in the present case, the nature proper to human intelligence.
“Now the intellective soul... holds the lowest degree among spiritual substances, in that it does not have, by nature, an infused knowledge of the truth, like the angels, but it must pick it up from material things through the senses.”
“As experience shows us, as long as the soul is united with the body, it can know nothing except by turning to the images of sensible things.”  By itself intelligence is like a blank slate. It can only form concepts from the world around it.
“So the intellective soul had to have not only the virtue of understanding but also the virtue of feeling. However, the action of feeling can only be done with a bodily instrument. It was therefore necessary that the intellective soul be united with such a body which could be the suitable organ of sense.” 
The realistic analysis of human intelligence, its functioning, its limits, therefore shows us that the union of soul and body is a necessity of nature. “It is for the benefit of the soul that it is united to the body and that it knows by turning to images of sensible things.” 
Thinking back on the religious message of metempsychosis: souls experience a succession of earthly lives in expiation for their past faults. But for a punishment to be meaningful, the perpetrator needs to remember some of the offending acts. And indeed, although the case is rare, people do claim to remember their past lives.
Mr. Paco Rabanne assures us, for example, that he was part of the conspiracy that attempted the assassination of Tutankhamun, in Egypt, and that he remembers the smallest details of the matter.  Fine! But what is memory?
If it is a sensible faculty, therefore linked to the body, should it not disappear with it? And if it resides in intelligence, can it retain sensible and tangible memories, such as colors, smells, circumstances of time and place? St. Thomas solves this difficulty in article I, q.79,a.6.
“Memory” can be understood in two ways. In the broad sense, it is a faculty whose function is to keep track of things. The very act of knowing is that the cognitive power possesses in it, in a way, the object itself.
Now we well know from experience that, even after leaving the known thing, we keep the impression of it within us. We can bring back to the field of consciousness such an idea, such a truth.
From this point of view it can be said that there is a memory in the intelligence, which is nothing other, in fact, than the intelligence itself. When it is no longer in contact with its object, it retains the knowledge that it had of it, at least latently. It can reconsider it at will.
But let's note right away that this is a power can only keep what it has received. If I put such information into a computer memory, that is the information it will keep. But intelligence is a spiritual faculty. The ideas it possesses are abstract, free from any consideration of time and place.
In a person, for example, intelligence considers only its human nature, its universal traits, not hair color or the tone of voice. Only sensible memory, linked to physical matter, receives and retains these concrete circumstances.
But remembering is not just considering one thing in ourselves, with the information we have received from it in the past. It is looking at its relationship to the past. Memory, in the strict sense, is about the past as the past. It consists of locating this thing in the past.
These qualities appear to me as those of something that is no longer, but was at a certain point in time. Memory, in the strict sense, is concerned with this circumstance that is time. But clearly, the past is substantive in nature, linked to matter. In this sense, memory does not lie in the intelligence, but in the sensibility related to the constitution of the body.
Thus, even if the reincarnation were true, strictly speaking, it would be impossible to remember such concrete events from our past lives. Each change of body would destroy ipso facto all the particular information received in the completed life.
 I, q. 76, a. 5.
 I, q. 89, a. 1. See also I, q. 84, a. 7.
 I, q. 76, a. 5.
 I, q. 89, a. 1. In this article, St. Thomas goes so far as to say that the union of soul and body is so intimate that the knowledge of the soul united to the body is more perfect than that of the soul in a state of separation.
 Annick Lacroix, “Is reincarnation possible?” Madame-Figaro, July 1989, p. 87.