<img height="1" width="1" style="display:none" src="https://www.facebook.com/tr?id=1906385056278061&ev=PageView&noscript=1" />
Skip to main content Accessibility feedback

Aquinas on the Occult

The Angelic Doctor wasn’t as opposed to what we now call the occult as you might imagine

Jimmy Akin

When people think of the occult, things such as astrologers, mediums, witches, and demons come to mind. Many dismiss such things as incompatible with modern science, and although Christians know the supernatural is real, it’s easy to be affected by this skeptical attitude.

But in the past, intellectual giants such as St. Thomas Aquinas took occult phenomena seriously. Back then, the word occult had a different meaning. In Latin, occultus meant anything that was hidden, anything that people didn’t know about or understand. The world thus was filled with “occult,” or hidden, things and forces.

Occult then had a neutral meaning, and so these weren’t necessarily contrary to the Faith. Just because men didn’t understand something didn’t mean it was evil.

God was the one who set up the world, and he created many things hidden from man’s knowledge. Sometimes he revealed these through the prophets and thus provided “occult” knowledge. Thus, Scripture says that God “reveals the things that are hidden [Vulg., occulta]” (2 Macc. 12:41).

Occult forces

Modern science recognizes four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. The first two were imperfectly understood in Aquinas’s day, and the latter two were unknown.

People knew objects fall, but they didn’t use gravity to explain that. It wasn’t till the 1600s that Isaac Newton proposed an invisible force causing objects with mass to attract each other. He named the force gravity from the Latin word meaning “heaviness.”

Newton got pushback, because the physics of his day held that bodies couldn’t influence each other unless connected by a physical medium. Gravity was supposed to work even across a vacuum, with objects exerting spooky action at a distance, so Newton was criticized for proposing this magical, “occult” force.

By contrast, Aquinas held that stones fall toward the Earth because they contain the element of earth (Letter on the Occult Workings of Nature [LOWN]), and though electricity and magnetism had been known since ancient times, it was not understood that they were two aspects of a single force.

Aquinas even listed magnetism as an occult force: “Now in the physical order, things have certain occult forces, the reason of which man is unable to assign; for instance, that the magnet attracts iron” (Summa Theologicae II-II:96:2 obj. 1).

Other objects also had natural abilities. Thus, Aquinas held that gold could improve mood and sapphires could stop bleeding (LOWN)—a parallel to modern “crystal healing.” The way these worked was hidden, but that didn’t make it wrong to employ them: “There is nothing superstitious or unlawful in employing natural things simply for the purpose of causing certain effects, such as they are thought to have the natural power of producing” (ST II-II:96:2 ad 1).

But there was a problem if you were adding magical or superstitious observances to an object’s natural abilities.


The word magic (Latin, magia) comes from the Magi, a Medo-Persian tribe with priestly duties. Originally, “magic” referred to the rituals Magi performed, but it was extended to any foreign or unauthorized rituals.

Magus (“magician”) then was applied to people who performed such shady rituals, no matter what their nationality—even Samaritans and Jews (Acts 8:9, 11, 13:6). It’s thus hard to say to what nation the Magi who visited Jesus belonged; we know only that they came “from the east” (Matt. 2:1).

In the first century, fields of knowledge we take for granted were not clearly distinguished. Religion, philosophy, science, medicine, and magic were combined in a confusing way. By Aquinas’s day, the distinctions were becoming clearer, and he contributed principles that helped distinguish them.


Our word pharmacy comes from the Greek pharmakon, which could mean a magic potion, a medicine, or a poison. Whichever of the three you wanted in the ancient world, you’d go to a pharmakeus, who would concoct it for you—illustrating just how tangled magic and medicine (and crime) were.

The practice of making such substances was known as pharmakeia. This is the word the New Testament uses when Paul lists sorcery as one of the “works of the flesh” (Gal. 5:20) and when John says that the nations were deceived by sorcery and that people did not repent of their sorceries (Rev. 9:21, 18:23).

This negative attitude toward pharmakeia was because it involved magic. Ancient pharmacists didn’t just grind up herbs to make medicine. They also recited spells and performed magical procedures over them.

This continued in the Middle Ages, and herbology was viewed with suspicion. Yet some plants had curative powers, and Scripture acknowledges that “the Lord created medicines (pharmaka) from the Earth” (Sir. 38:4)—so there had to be something good here. The question was how to disentangle medicine from its magical overlay.

Aquinas acknowledged that it’s permitted to use a substance’s natural effects, “but if, in addition, there be employed certain [mystical] characters, words, or any other vain observances which clearly have no efficacy by nature, it will be superstitious and unlawful” (ST II-II:96:2 ad 1).


Astronomy and astrology were indistinguishable in the Middle Ages, but it was clear they contained a mix of truth and falsehood. Aquinas knew some things could be predicted with certainty, “even as astrologers foretell a coming eclipse” (ST II-II:95:1), but not everything astrologers said was true.

It’s surprising how open medieval individuals were to astrology. The heavenly bodies had been regarded since antiquity as having a great deal of influence on Earth. Thus, in medicine, herbologists would pick or prepare plants when the heavenly bodies were in certain alignments to ensure their potency (a practice not wholly without basis, since plants ripen in different seasons, though that has to do with the sun rather than the moon or planets).

Aquinas was prepared to see the stars as influencing physical bodies: “The natural forces of natural bodies result from their substantial forms, which they acquire through the influence of heavenly bodies; wherefore through this same influence they acquire certain active forces” (ST II-II:96:2 ad 2). But he denied that one could create “astronomical images” imbued with power from the stars by inscribing astrological signs on them. The reason was that the signs are artificial.

The stars might give a magnet its ability to attract iron, but men could not channel the power of the stars by inscribing symbols on an image, since such characters “do not conduce to any effect naturally, since shape is not a principle of natural action.” Consequently, “no force accrues to them from the influence of heavenly bodies, in so far as they are artificial.” Only the natural substances of which they were made might have an effect (ibid.). Because the stars influenced the physical world, Aquinas held that “astrologers, by considering the stars, can foreknow and foretell things concerning rains and droughts” (ST II-II:95:1).

But what effect did the stars have on man? In antiquity, many thought the stars rule our fates inexorably, but Christian thinkers held that this wasn’t compatible with free will. Although it was men’s choices that determined their destiny, this didn’t mean the stars had no influence. Since they were physical objects, stars couldn’t affect our souls directly, but they could affect our bodies and the sensations we experience, such as anger and concupiscence. They thus could influence the choices we make, for “the majority of men follow their passions, which are movements of the sensitive appetite, in which movements of the heavenly bodies can cooperate” (ST I:115:4 ad 3).

Aquinas didn’t regard making predictions on this basis as the sin of divination, because they were natural predictions based on human reason: “Accordingly, it is not called divination, if a man foretells things that happen of necessity, or in the majority of instances, for the like can be foreknown by human reason” (ST II-II:95:1).
It would be superstition, though, if “by observing the stars, one desires to foreknow the future that cannot be forecast by their means,” and thus “we must consider what things can be foreknown by observing the stars” (ST II-II:95:5).

Since most men follow their passions, Aquinas concluded that “astrologers are able to foretell the truth in the majority of cases, especially in a general way. But not in particular cases; for nothing prevents man resisting his passions by his free will” (ST I:115:4 ad 3).

But since few resist, astrologers were particularly able to predict “public occurrences which depend on the multitude” (ST II-II:95:5 ad 2), such as wars and the like.


Demons could influence physical objects, at least in certain ways, so Aquinas held they could intervene in human affairs.

Both the good and bad angels could assume temporary physical forms (ST I:51:2). These temporary bodies allowed them to perform some tasks but not others. For example, they could not reproduce—at least not directly.

However, following St. Augustine, Aquinas held that demons could take the forms of incubi and succubi and have relations with human beings. This would allow them to acquire the cells needed for reproduction: “If some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men taken for the purpose; as when the demon assumes first the form of a woman, and afterward of a man.” In this case, the offspring would be fully human, “so that the person born is not the child of a demon but of a man” (ST I:51:3 ad 6).

Demons’ control over physical bodies was limited. Again, following Augustine, Aquinas held they could not transform a human body into that of a beast, “since this is contrary to the ordination of nature implanted by God.” But demons could trick human senses into thinking a person had turned into a beast: “Imaginary apparitions rather than real things accounted for the aforementioned transformations” (On Evil, 16:9 ad 2). He thus saw werewolf-like transformations as illusions rather than physical events.

Aquinas didn’t have a problem with using hidden natural forces, but he was wary of practices that included words or other symbols. There was nothing wrong with invoking God, the good angels, or the saints, but the only other spirits that might respond to invocations were demons.

“In every incantation or wearing of written words [on an amulet or medal around the neck], two points seem to demand caution. The first is the thing said or written, because if it is connected with invocation of the demons it is clearly superstitious and unlawful. On like manner it seems that one should beware lest it contain strange words, for fear that they conceal something unlawful” (ST II-II:96:4).


The spirits of departed humans also could manifest in the world.

As did all medieval people, Aquinas recognized that the saints in heaven could appear to men, and he recognized that the same was true of other souls: “It is also credible that this may occur sometimes to the damned, and that for man’s instruction and intimidation they be permitted to appear to the living; or again in order to seek our suffrages, as to those who are detained in purgatory” (ST III-II:69:3).

The damned thus might appear—perhaps against their will—to scare the living back onto the straight and narrow, and those being purified might appear to seek prayers.

Natural human abilities

What power might the human soul have to influence physical things? Aquinas held that souls can affect their own bodies directly, and they can affect other things indirectly.

For example, “when a soul is vehemently moved to wickedness,” this might manifest in the eyes so that “the eyes infect the air which is in contact with them to a certain distance” and thus “the countenance becomes venomous and hurtful, especially to children, who have a tender and most impressionable body” (ST I:117:3 ad 2).
This was Aquinas’s explanation for the “evil eye,” and it was reasonable to fear a child might be harmed by it (ST II-II:96:3 ad 1).

Aquinas considers only the case of a person’s soul being moved by a desire to harm someone, not whether the same principle could be used for neutral or good purposes. However, he sees the soul as having at least a weak natural ability to produce physical effects remotely. Today, such natural mental abilities would be classified as psychic powers, and this specific ability would be a form of telekinesis.

He also acknowledged another natural human ability that today would be classified as psychic: precognition, which he referred to as “natural prophecy.”

In supernatural prophecy—or prophecy in the proper sense—God reveals something to a person, possibly through an angel. However, Aquinas held that humans also have a natural disposition allowing them to sometimes learn about the future.

He distinguished this from predictions based on learning and experience, such as how “the doctor foresees that health or death will come, or a meteorologist foresees the storm or fair weather” due to “technical knowledge” (Disputed Questions on Truth, 12:3).

Instead, natural prophecy “is derived from the power of created causes, in so far as certain movements can be impressed on the human imaginative power.” Given the influence he believed the stars have, it’s no surprise he saw them as one cause of these impressions, believing they can be produced “for instance, by the power of the heavenly bodies, in which there pre-exist some signs of certain future events.” Also, unlike supernatural prophecy, natural prophecy is not infallible “but predicts those things which are true for the most part” (ibid.).

Natural prophecy can occur in dreams, but it wasn’t the only reason dreams sometimes foretell the future.

Aquinas says they also may do so by chance or when a man responds to a dream to create a self-fulfilling prophecy. Alternately, predictive dreams may be caused by God, angels, or demons. But sometimes they are due to the natural “disposition of the heavenly bodies” (ST II-II:95:6).

Although Aquinas doesn’t explain in detail how to tell when this is the case, he notes that “we must say that there is no unlawful divination in making use of dreams for the foreknowledge of the future, so long as those dreams are due to divine revelation, or to some natural cause inward or outward” (ibid.).


Superstition is a vice contrary to religion that “offers divine worship either to whom it ought not or in a manner it ought not” (ST II-II:92:1), and Aquinas’s discussions of occult phenomena offer principles for discerning whether a particular practice is lawful or superstitious.

The first concerns whether the goal of the practice is good. If you’re trying to do something wrong—such as harm a child with the evil eye—the practice is not permitted.
The second concerns whether it can be expected to have an effect. If the practice can’t possibly work—like expecting an image to have power from the stars because you put an astrological symbol on it—it’s superstitious and thus not permitted.

The third concerns whether the practice works by natural means. If you’re relying only on powers God built into nature—like an herb’s healing effect—the practice will be lawful.

The situation is more complex if you’re explicitly or implicitly invoking a spiritual entity. The fourth principle thus concerns who you’re invoking. If it’s demons—whether you’re aware of that or not—the practice isn’t lawful. Even if you’re invoking God, his angels, or the saints, it’s not automatically legitimate, because it’s possible to invoke them superstitiously.

The fifth principle is thus checking that you’re being reasonable and reverent. For example, when considering whether it’s lawful to wear an amulet or medal with divine words written on it, Aquinas says, “one should beware lest, besides the sacred words, it contain something vain, for instance certain written characters, except the sign of the cross; or if hope be placed in the manner of writing or fastening or in any like vanity having no connection with reverence for God, because this would be pronounced superstitious. Otherwise, however, it is lawful” (ST II-II:96:4).

Sidebar 1:  The Medieval Cosmos

In the Middle Ages, it was thought that things on Earth were made of the four classical elements: air, earth, fire, and water. Everything else was a mixture of these four. The elements weren’t thought to be made of atoms but could be divided indefinitely, without reaching a smallest unit of matter.

Opinion was divided on the stars. Some thought the heavenly bodies were made of the same four elements, but others thought they were made of a fifth element called aether (cf. Summa Theologiae I:70:1 ad 1).

It was thought that the Earth was a sphere at the center of the cosmos. The heavenly bodies—the sun, moon, and stars—were thought to surround the Earth in a series of transparent, concentric shells or spheres.

The lowest sphere held the moon. Everything below the moon (i.e., the sublunar world) was subject to change and corruption. But since the heavenly bodies endlessly moved in their orbits, seemingly without change, they were regarded as incorruptible.

Outside the spheres was the highest heaven, sometimes called the empyrean heaven—a realm filled with light where the angels and saints dwell (ST I:61:4, I:102:2 ad 1).

The spiritual world contained beings Aquinas called separated substances—that is, things that exist though separated from matter. These included God, angels, demons, and disembodied human souls.

Sidebar 2: Aquinas on Evaluating Actions

It’s remarkable how free medieval society was of skepticism about mysterious phenomena. It’s also striking how willing figures such as Aquinas were to think carefully about what is acceptable and unacceptable. He didn’t simply dismiss everything as being due to demons or forbid everything that we would consider occult.

In subsequent centuries, we’ve made both scientific and doctrinal progress (CCC 2115-2117). Astron-omy and astrology have been disentangled. Also, medicine and magic are largely distinct, though quack procedures relying on allegedly spiritual principles (e.g., Reiki) remain.

In some ways, our age has become too quick to dismiss accounts of the spiritual and paranormal. Aquinas may have been wrong about the influence of the stars, but the world nevertheless has hidden elements.
These include the supernatural forces Christians have long been aware of. They also include natural things science hasn’t discovered (e.g., some scientists think we may have found evidence of a fifth, previously unknown, fundamental force).

Aquinas made a real contribution with his principles for discerning the good and the bad in mysterious phenomena, and these remain valuable as we encounter the many mysteries God’s world still contains.


Enjoying this content?  Please support our mission! Donate