Philosophy and the Immortality of the Human Soul: A Tool for the New Evangelization

Problem: There is a need today for the argument for the immortality of the human soul based on reason alone for both believers and non-believers.

The first pages of Scripture allude to the nature of the human soul when the inspired writer tells us that God “breathed into his nostrils the breath of life, and man became a living soul,” and that man is made in the “image and likeness” of God. 1 It is apparent that the proper interpretation of these verses is important for understanding the nature of man and, consequently, what his dignity and destiny are. The “Theology of the Body” is a popular interpretation today, with its rich insight into the first few chapters of Genesis. But, surely there is also a pressing need for a “philosophy of soul,” shedding light on the same passages. One of the truths which can be recognized, as revealed by the first chapters of Genesis, is the immortality of the human soul, a quality of the creature made after the image and likeness of God.

Why Philosophy?
Although the doctrine on the immortality of the soul is knowable through the supernatural light of faith, it can also be known philosophically through the natural light of reason. In his grand encyclical, Fides et Ratio, Blessed John Paul II proclaimed the need for a strong and rigorous philosophy which can respond to the most profound questions proposed by the human experience, lest people of our time (especially the young) stumble through life without foundation or any valid points of reference. 2 He challenges philosophers to address these most profound questions—which have an important relationship to the Christian faith—including the desire of men to know what happens after death:  “We want to know if death will be the definitive end of our life or if there is something beyond—if it is possible to hope for an after-life or not.” 3

This natural knowledge of the immortality of the soul, part of what are traditionally known as the “preambles of the faith,” can reinforce the legitimacy of the basic questions answered by the Christian faith—such as: what happens to the soul after death?—and reassure believers in their most basic convictions.

In addition, this question is important for unbelievers, and for the “New Evangelization,” because the knowledge that my soul will survive after death can act as a springboard to faith. If natural reason tells me there is something beyond, the role played by a religion, which claims it can shed light on this “beyond,” becomes more significant. Many in our society have succumbed to a practical materialism which implicitly denies the existence of anything immaterial, which eliminates a priori questions which transcend scientific experimentation—such as God, and the soul—as rationally indemonstrable. These are locked within the confines of their own “immanence without reference of any kind to the transcendent.” 4 To this error we hope to present an argument, aided by philosophical reasoning, which proves that the soul of man continues to exist after separation from his body. We hope to aid priests in their task of preaching on this basic truth, so that they may both fulfill the believers’ need for a “natural, consistent, and true knowledge of created realities,” called for by Blessed John Paul II, and inspire in unbelievers the pursuit and hope of eternal life. 5

The Objections
There are many objections against the immortality of the soul, and this brief article will not pretend to exhaust them. We will, however, attempt to address an objection which seems to be commonly held today, rooted in that scientific materialism which denies the existence of any immaterial realities, or at least disregards them as beyond the scope of legitimate “rational” inquiry, limited to scientific positivism. This objection denies the existence of the immaterial soul by arguing that all the operations of the human person, including the highest intellectual activities, can be explained by our bodily functions. The ever-increasing knowledge of the complexity and sophistication of the brain, provided by neuroscience, lends credence to this position. It rejects the key proposition that intellectual activity is immaterial, which necessitates the subsistence, and immortality, of the soul. If true, the objection invalidates this argument for the immortality of the soul.

There are reasonable arguments for this objection put forward by intelligent people. For instance, when someone has a lobotomy, or takes psychotropic drugs, their thinking is seriously impaired, or removed all together. Would not this argue in favor of the position that intellectual thought is solely a function of the brain? What can be said to defend the immateriality of intellectual thought?

Another objection which might be raised against this argument concerns its practical pastoral applications. Some might object whether a fairly sophisticated philosophical proof such as this would really be a useful tool for the New Evangelization. Isn’t the complexity of the argument beyond the grasp of most people, given the necessary background in philosophy required to perceive the argument’s validity? This is another legitimate objection. After presenting our argument, we will address these difficulties.

The Argument for the Immortality of the Human Soul
This question has been traditionally answered by studying the nature of the actions specific to man, particularly intellectual thought. We will consider here the argument as enumerated by St. Thomas Aquinas. It relies upon the Thomistic theory of knowledge, which we also propose as a compelling and reasonable system for making sense of man’s intellectual activity, and coming to grips with the first objection raised above. The argument depends upon the fact that something’s action follows upon what that thing is; when we see a frog hopping, breathing, and eating, we know something about what it is, that it is living and having a source of motion in itself. In a similar way, we can know something about what our human intellect is by considering what it does.

St. Thomas’ proof rests on the proposition that a man’s intellectual activity is not the act of a bodily organ.6 This is because a man thinks intellectually in a mode which is universal, necessary, and immaterial. He is able to grasp the unchanging essence of a thing, what the thing is, its quiddity. This essence is universal, meaning it is the same for all intellects—human, as well as angelic, and even Divine! It is also necessary, which means that it cannot be otherwise. The nature or essence of a circle is the same for all intellects who have true knowledge of what a circle is—which according to the human mode of speaking can be defined as a round figure whose boundary consists of points equidistant from the center. If its nature were otherwise than what it is—for example, if the boundary of the figure consisted of points which are not equidistant from the center—it would no longer be a circle; hence, the force of necessity that the true knowledge of a thing’s essence obtains. Here, we are dealing with the question of “universals,” which has occupied the minds of philosophers for centuries. Due to the nature of this article, we can offer only a cursory explanation of this question. Suffice it to say, that if one denies that human persons are capable of real knowledge of things outside of themselves, according to the human mode of knowing—the knowledge of universal essences—one is crossing into an interminable philosophical labyrinth.

The critical fact that intellectual thinking must be immaterial will be explored further below. If his intellectual activity is immaterial, it follows that the source of that activity, the soul or mind, must itself be immaterial because a thing’s action follows upon what it is. Thus, the source of this immaterial activity must, in some sense, exist of itself, not being a part of the body since its act is not the act of a bodily organ. Now, anything that does not have a material body cannot corrupt because only something composed of matter corrupts when the matter decays. When the matter of the human body corrupts, the soul must continue to exist.

This argument stands or falls on the proposition that man’s intellectual activity is immaterial. How can this be proven? We must take a closer look at the act of thinking. This is an extremely complicated process, and difficult to understand—one could easily study the Thomistic theory of knowledge for years without exhausting the subject. The rudimentary sketch we are giving must not be taken simplistically, as anything close to a complete exposition of Thomas’ doctrine of knowledge, but as a broad outline, limited by our purposes here.

For St. Thomas, the senses act as gateways of knowledge: there is nothing in the mind that was not first in the senses. It is the process by which knowledge passes from the senses to the intellect which necessitates that intellectual knowledge be immaterial. This is accomplished through abstraction, which renders the potentially intelligible sense data in the mental image, or “phantasm,” actually intelligible by separating the essence or nature of the material object presented by the phantasm from its individuating matter. This specific nature, or essence, which is the universal form or idea of the thing apart from its individuating notes, is then received by the intellect in this universal, immaterial mode. 7

It is the active intellect which renders actually intelligible the universal nature, or form, individualized in the material object presented by the phantasm. The relationship between the active intellect, and the intelligible species, can be analogously compared to the relationship between the faculty of seeing, and the light by which one sees an object. Just as color, which is the object of sight, is made actually visible only by the illuminating power of light, so the intelligible species, contained potentially in the image or phantasm, becomes actually intelligible when illumined by the agent intellect.8 Thomas holds that this light of the agent intellect is a participation in the Divine intellectual light.

What exactly is the phantasm, and how does it differ from the immaterial, intelligible idea which is imprinted on the intellect? This key distinction separates material sense knowledge from immaterial intellectual knowledge. 9 The phantasm may be referred to as the “mental image” of the object known. However, it is more than a replica of sense data received from the faculty of seeing, or of any other individual sense. It is the result of an extremely complex process of uniting the various modes of sense knowledge, both internal and external, into a certain integration of sense data. 10 It acts as a sort of intermediary between sense knowledge of the object individuated in particular matter, and the universal knowledge of the idea or concept. 11 However, the phantasm is still on the level of sense knowledge of a particular object, and, thus, necessarily involves the material considerations of space and time. 12

In order to abstract the universal idea from the particular sense knowledge represented by the phantasm, the agent intellect must “consider the nature of the {intelligible} species apart from its individual qualities represented by the phantasm.” 13 It reveals the intelligibility of the thing represented by the phantasm by neglecting the matter which individualizes the form, and considering only the universal form. The resulting universal and immaterial form, also called the intelligible species, is then imprinted on the passive intellect in the same immaterial mode, since the thing known is in the knower, according to the mode of the knower. 14 So, the form of “man” both exists individualized, materially, in the particular flesh and bones of the man, Socrates; and universalized intentionally and immaterially in the intellect of Plato, who is thinking about Socrates as a “man” in the abstract. The idea of a circle exists in its individual particularity on the student’s geometry paper, with its particular size and color, and universalized intentionally and immaterially in the student’s intellect, which allows her to consider the qualities of all circles, regardless of their particular colors or sizes. Thus, the mode of the idea existing in the intellect is universal and immaterial, abstracted from matter, so the intellect, which is united to the idea, must also be immaterial in order to receive this idea.

Answering the Objections
We have attempted to address, above, the general objection that man’s intellectual activity can be explained by the brain alone, by showing that this intellectual activity must be immaterial, and thus must be derived from an immaterial principle—it cannot be the act of a corporeal organ. The more specific objection still needs to be answered, which states that, if intellectual thinking is altered or impaired by altering the brain, it must be an act of the brain. As is so often the case, Thomas addresses this very question in the Summa, noting that when a corporeal organ suffers a lesion, which impedes the imagination, or the memory is hindered through lethargy, a man is hindered from actually thinking. 15 This is not because the intellectual act is an act of a material organ, but because the intellect, for its act, requires the action of another power that does make use of a corporeal organ. We have already seen this in our discussion of the phantasm, which is a product of sense data gathered through the corporeal senses. The phantasm acts as the raw material for the intellect to operate upon. If the production of the phantasm is impeded or altered, it would follow that the functioning of the intelligence would be impeded, since the raw material of the intellect would be either confused or removed altogether. Thus the detrimental effect of psychotropic drugs, or a lobotomy, on the intellect gives evidence that the brain is used instrumentally in the intellectual act, but it does not demonstrate that the act of thinking is itself an operation of the brain. So, this objection does not prove that intellectual thinking can be explained by the brain alone, but that it requires the brain to function properly as the primary material instrument for human thinking to actually occur. Although seemingly quite simple, this answer again rests upon the complex and sophisticated philosophy of human knowledge which we have tried to outline in this article.

Concerning the objection that this argument is not really pastorally helpful because of its intellectual sophistication, there are a few possible responses. First, if the argument is presented well, there is no reason why it may not appeal to some, particularly to the intellectually inclined, and to those who are searching for the truth through philosophical enquiry. It is all too often the case that philosophical arguments, derived from Thomism, are not known sufficiently (if at all) at university level philosophy, so that many who may not have encountered the argument before, may find it compelling. This is one good reason for its rediscovery and promotion. This argument will also often be in accord with the confused knowledge derived from basic human reflection, and could be recognized as the articulation of a position implicitly held. However, even if someone is unable to grasp the argument for the immortality of the soul, the assurance that this is, at least, capable of being proved on the grounds of reason alone, can act as a kind of buffer to faith, on a certain psychological level, and guard against naïve fideism. For catechists and priests, to whom this argument should be more accessible, given their philosophical background (at least for priests), it could be very helpful in reassuring their own convictions. Those whom they teach and minister to will certainly sense, and find more nourishment, in their convictions the more deeply they are held. There are many other objections, as we have mentioned, and to these there are other answers—many of which can be grounded upon St. Thomas’ theory of human knowledge and his philosophical anthropology as a whole.

We believe that the argument for the immortality of the soul, based on philosophical reasoning alone, is an extremely useful aid, both to provide a rational grounding for those who hold this basic doctrine on faith, as well as for the New Evangelization. The proof relies on the argument that the intellectual power in man cannot be the act of a material organ, because the idea, or concept, is present in the intellect in a universal, necessary, and immaterial mode, through the process of abstracting the essence from the material particularities of the phantasm. Although this is a very complex process, the theory of knowledge, taught by St. Thomas Aquinas, gives a satisfactory and reasonable account of it, specifically his presentation of the relationship between sense and intellectual knowledge. There are other arguments for the immortality of the soul: for example, Adrian Reimers includes in his recent work on the soul the fact that hypothetical reasoning (one of the foundations of modern science) “has the character of a leap, an intellectual connection, of what was previously unconnected” which he argues cannot be accounted for by a mechanical, physical operation. 16 He also argues that language, logic, and signification, in general, in the experience of human persons, are evidence of an immaterial rational principle, and, therefore, the immateriality and immortality of the soul.

Since our highly scientific and technology-driven culture tends to consider only those things immediately accessible to the senses, and receptive of material experimentation, the validity of these arguments could be passed over too quickly. However, they should be given their proper place, especially, since the “preambles of the faith” have traditionally played an important role in the Church’s evangelization efforts. Since they ask a person to consider arguments concerning the highest truths knowable through reason and common sense alone, they may be a very helpful means of bridging the gap between agnostic prejudices against the faith, and that journey of questioning and thinking which ends under the guidance and grace of the Holy Spirit, in a rationally grounded act of faith. They certainly ought to be familiar to those who form others in the faith, both to pass on these treasures of our intellectual heritage, as well as to strengthen their own conviction and witness.

  1. Genesis 1.27 and 2.7.
  2. See Fides et Ratio, 6, at
  3. Fides et Ratio, 26.
  4. Fides et Ratio, 81.
  5. Fides et Ratio, 66: “It is necessary therefore that the mind of the believer acquire a natural, consistent, and true knowledge of created realities—the world and man himself—which are also the object of divine Revelation. Still more, reason must be able to articulate this knowledge in concept and argument. Speculative dogmatic theology thus presupposes and implies a philosophy of the human being, the world and, more radically, of being, which has objective truth as its foundation.” Note that he claims this “natural, consistent” knowledge is necessary for the believer, which we take to refer to the ordinary believer in the pew, rather than solely the professional theologian or philosopher.
  6. This argument is taken from ST Ia, Q. 75, a. 2., c. See also Ashley, Benedict, The Way Toward Wisdom: An Interdisciplinary and Intercultural Introduction to Metaphysics (University of Notre Dame Press, 2006), pp. 106 and 107, as well as Gyula Kilma, “Aquinas on the Materiality of the Human Soul and the Immateriality of the Human Intellect,” Philosophical Investigations 32:2 (April 2009), pp. 163-182, and Garrigou-Lagrange, Reginald, Reality: A Synthesis of Thomistic Thought (Ex Fontibus Co., 2006), pp. 151-152.
  7. Sheen, Fulton, God and Intelligence in Modern Philosophy (University of Louvain, 1925; reprinted Wipf and Stock, 2009), p. 112.
  8. Gardeil, H.D., Introduction to the Philosophy of St. Thomas Aquinas v.3: Psychology, tr. J. Otto (Herder, 1963; reprinted Wipf and Stock, 2009), p. 131.
  9. See Ashley, Benedict, Choosing a World-View and Value System (Society of Saint Paul, 2000), pp. 161-162.
  10. Gardeil, pp. 129-130.
  11. Ibid.
  12. For a helpful proof why knowledge of the singular must be material, see Gyula Kilma, “Aquinas on the Materiality of the Human Soul and the Immateriality of the Human Intellect,” Philosophical Investigations 32:2 (April 2009), pp. 176-177.
  13. Summa Theologiae, Ia, Q. 85, a. 1, ad. 1.
  14. Ibid., Ia, Q. 12, a. 4, c.
  15. Ibid., Ia, Q. 84, a. 7, c.
  16. Reimers, Adrian J, The Soul of the Person (Catholic University of America Press, 2006), p. 267.
Bookmark and Share
avatar About Br. John McCusker, OSB

Brother John McCusker, O.S.B., is a Benedictine monk of Saint Louis Abbey in St. Louis, Missouri, and is currently studying for the priesthood at the Dominican House of Studies in Washington, D.C. He is a graduate of the University of Notre Dame, Indiana.


  1. avatar Darren O. says:

    Dear Br. McCusker:
    The soul is dead with out God’s grace. An individual human can only regain God’s grace through the sacraments provided for that purpose by the Divine Son, Jesus Christ. How can a philosophical argument demonstrate the living presence of something that is in fact dead?* It can not. Simple logic. Your opponents have spoken the truth, their souls are (practically) non-existent. For them the most apt model of thought might be mechanical or brain based. It is, at least, an honest appraisal of their state of being, if it is not an honest appraisal of what their lives could be. We know that the fault lays with their rejection of the life of grace, but the aqueduct carrying the life giving waters to them has been smashed for some many centuries now. That they survive at all is only because God, in His mercy, sends the occasional rain so the mud they live in doesn’t totally dry out. If you would, in God’s Charity, have them live again should we not begin to clear away and properly bury the corpses that litter the roads and waters Europe thanks to the misanthropy of les philosophies? In other words, what sense does it make to attempt a philosophical program of the utmost importance to our understanding of the soul, w/o including God in the discussion? It is really just too bad for the opposition to this program if they don’t like talking about God. No point in jazzing up the window dressing. It prudent to stamp God on the outside of the package because it’s going to be more talk of God on the inside.

    The cure for the disordered state of philosophers isn’t more philosophy. The cure for philosophy is what it always has been and ever will be, dear Brother McCusker, the Grace of God.

    *One might be able to infer or imagine the life lived based upon reasoning about a particular corpse, but that will not re-animate the corpse. Similarly, from a living man, you might be able to infer the life of the soul even when it is absent or dead, but no mere man can bring the soul back to life. If you wish people to grasp that there can be the life of the soul, then you must have that life to show them in the first place and show them the way so that they too can gain this new life. Which brings you right back to teaching what the Church has always taught. The new evangelization is the same thing as the old one.

  2. avatar Br. John McCusker says:

    Dear Darren,

    Thank you for your comment. I think you are a bit confused… a soul which is not in the state of grace is dead according to the life of God and as directed to its supernatural end, but human nature still remains what it is. Otherwise those who are not in the state of grace would be physically as well as spiritually dead. The (important) question whether a soul is in the state of grace does not effect the question whether the human soul is naturally immortal. With or without grace, the soul continues to exist after separation from the body, and this can be proven using philosophy alone. The argument is significant because those who do not accept the faith might be open to this rational demonstration.

    As for the role of philosophy, the practice of orthodox Catholics from the time of the Fathers of the Church has been to make full use of what is good and true according to right reason in explaining, defending, and propagating the faith. I agree that grace has an important role to play in the cure of disordered philosophy, but so does a properly ordered philosophy. For an exposition of the Church’s mind regarding the relationship between faith and reason, you need look no further than John Paul II’s encyclical “Fides et ratio.”

    • avatar Martin B. Drew says:

      Dear Brother McCusker Your article was excellent. St Thomas Aquinas used Aristotle’s metaphysics and concepts to aid him and his students at the U of Paris in studying and forming his theological, doctrine and moral tracts. I studied this theology and philosophy at the University of Dallas and St. Mary’s seminary Perryville, Mo and the Lateran in Rome obtaining a licentiate in them and Scripture. Bishop Sheen wrote a book in 1925 ” God and intelligence in modern philosophy “. This is a good read for non-believers. God bless you. Martin Drew Dallas Tx.

  3. avatar Fr. Walter Macken says:

    St. Thomas had the answers all right, hadn’t he? There is one phrase of his I picked up. The human mind is capable of activities which are intrinsically independent of matter while being extrinsically dependent on sense information. There is also an immense argument for the immortality of the soul in Plato’s Apologia in the discussion Socrates had before his execution . That was 400 years before Christ! Socrates knew that the soul was immortal and could not be reduced to brain activity.

  4. avatar Darren O. says:

    Dear Brother John:
    OK, you think (suspect?) I am confused. Fair enough. In charity, you have left the door open by suggesting a degree of uncertainty as to if I am in fact, confused. Perhaps I should not write any further, paraphrasing Mark Twain, and remove all doubt.

    But being a fool… let me approach this from another angle. Your subheading “Problem: There is a need today for the argument for the immortality of the human soul based on reason alone for both believers and non-believers.” is like saying let’s come up for an argument for breathing as if air was irrelevant to the discussion. You won’t even finish the first airless breath before being forced to consider air in the discussion. If the many atheists we come across refuse, invoking Bill Clinton, to agree even on “what is is,” then the fault we face in dialog with them rests not in philosophy. No general in battle will think he is winning because he successfully retreated. Indeed, Christianity can not, even for one second,sustain it’s position without recourse, in prayer and definition, to God and grace. In hoc signo vinces, bonum frater Johannes.

  5. avatar Nick says:

    I think this is an absolutely crucial discussion to be having, since this is a preamble to be able to be talking about Natural Law. In Pope Leo’s XIII famous Encylical on human Liberty, he begins in the first few paragraphs by saying:
    “The unanimous consent and judgment of men, which is the trusty voice of nature, recognizes this natural liberty in those only who are endowed with intelligence or reason; and it is by his use of this that man is rightly regarded as responsible for his actions. For, while other animate creatures follow their senses, seeking good and avoiding evil only by instinct, man has reason to guide him in each and every act of his life. Reason sees that whatever things that are held to be good upon earth may exist or may not, and discerning that none of them are of necessity for us, it leaves the will free to choose what it pleases. But man can judge of this contingency, as We say, only because he has a soul that is simple, spiritual, and intellectual – a soul, therefore, which is not produced by matter, and does not depend on matter for its existence; but which is created immediately by God, and, far surpassing the condition of things material, has a life and action of its own so that, knowing the unchangeable and necessary reasons of what is true and good, it sees that no particular kind of good is necessary to us. When, therefore, it is established that man’s soul is immortal and endowed with reason and not bound up with things material, the foundation of natural liberty is at once most firmly laid.”
    His proof is more ‘practical’ rather than philosophical, but I think it gets the ball rolling. Man is obviously not like the other animals in that man has some kind of higher power, namely the use of Reason. No other animal can do this, despite the fact our dna is not radically different; the very ability to reason transcends chemical reactions in the brain


  1. [...] MORNING EDITION Published November 21, 2012 Anno Domini Philosophy & Immortality of the Soul: New Evangelization Tool – Br. John McCusker [...]

  2. [...] Philosophy and the Immortality of the Human Soul: A Tool for the New EvangelizationThe first pages of Scripture allude to the nature of the human soul when the inspired writer tells us that God “breathed into his nostrils the breath of life, and man became a living soul,” and that man is made in the “image and likeness” of God. 1 It is apparent that the proper interpretation of these verses is important for understanding the nature of man and, consequently, what his dignity and destiny are. The “Theology of the Body” is a popular interpretation today, with its rich insight into the first few chapters of Genesis. But, surely there is also a pressing need for a “philosophy of soul,” shedding light on the same passages.…more [...]

NeverWinter Astral Diamonds