Thomistic Philosophy: An Introduction

St. Thomas Aquinas (1225–1274) was a systematic thinker. He developed his philosophy and theology within an intellectual framework called metaphysics. In our times it seems necessary to add that he worked within classical metaphysics, the one founded by Aristotle. It is hard to understand Aquinas’s arguments without knowing the principles of classical metaphysics. There are many intellectuals who quote Aquinas in order to support their own theses which may or may not actually fit into his system. But how can we judge whether a given concept harmonizes with Aquinas’s thinking? The answer can be found in metaphysics: if the idea does not comply with classical metaphysics it cannot belong to Aquinas either. This is also why one cannot understand Aquinas without knowing metaphysics. It is similar to any other discipline of knowledge: One cannot just jump into understanding Einstein’s general relativity without knowing the basics of classical mechanics; one will not understand mathematics without algebra, or microbiology without knowing chemistry. Metaphysics in Aquinas is like algebra in mathematics – one needs to understand it to be able to follow Aquinas’s arguments.


Metaphysics is not alchemy or astrology as sometimes people tend to see it. Metaphysics is the “science of being”, that is, a philosophical discipline that describes being at the basic or the most abstract level. We can say that metaphysics deals with being as being, or, in other words, being as such (per se). What does it mean to consider being as being? Perhaps, prior to addressing this question we should ask what being is. And this question is already a part of metaphysics. Any such “impractical”, “abstract” and apparently “useless” question most probably belongs to metaphysics. It is because metaphysics does not serve any other natural discipline of knowledge. It is selfless; we learn metaphysics in order to know the ultimate reality, or to gain wisdom. Metaphysics does not help improve technology or make our life easier. Unlike other disciplines, metaphysics does not have any immediate application in any other field of our activity. Here we come to the first principle of metaphysics (and any true philosophy for that matter) which is selflessness. If one looks for practical answers one should not weary himself with metaphysics. But if one looks for truly wise and ultimate answers in the order of natural reason then metaphysics is the place to go.


So, what is being? Imagine something that simply exists, without any qualification. Something that simply is. Can you do this? I presume not. In fact no one can imagine being as such, because whatever we imagine it is already somehow defined, categorized. If you think of being as a vast grey substance it is already vast and grey. If you think of it as a point or an idea you always imagine it under some categories. Being as such is incomprehensible. This, however, does not render our effort useless. In fact many disciplines of knowledge deal with objects which are invisible or even unimaginable. In mathematics, for instance, we use infinity. We cannot imagine infinity, because whatever we imagine is finite. But we understand the notion of infinity and we have a symbol to signify it. Similarly, in metaphysics, even though we cannot imagine being, we can conceive and understand what we mean by the word “being” (per se).

Real and Ideal Being

Being is all what exists. The most tangible examples of beings are objects around us. We see them, we can touch them. We know they exist. But there are also beings that we cannot see. Perhaps in the neighboring house there are chairs and tables similar to the ones in your house. You can’t see them, but if you visited your neighbor in the past and you saw them, now you can imagine they are still there. It might have happened, though, that your neighbor discarded his furniture. His chairs do not exist anymore; they were chopped and burnt. You have memory of them. Now they do not exist in reality any more, but in your mind or imagination only. Hence the first crucial distinction – things that exist in reality (exist actually) and those that exist only in thought (exist ideally or potentially). For Aquinas and classical metaphysicians only the real existence is a “true” existence. Existence in thought is not real, therefore it is not existence. Beings in our minds are only in our minds but not in reality and for this reason we cannot say they actually exist. We say they exist only potentially, that is, they could exist (your neighbor could have saved his chairs) but they do not (the neighbor actually destroyed them).

Material and Immaterial Being

Chairs and other objects we perceive with senses are material. We call them bodies. All things that are material are bodies in a metaphysical sense. But not all things that exist in reality are bodies. There are also beings which are not material yet really exist, not just as ideas in your mind but in a completely real way, outside of your mind and imagination. In metaphysics these are called pure substances, detached substances or spirits. Detached in this context means they are detached from matter. “Pure” means that they have nothing to do with matter and accidents. For us humans, who naturally learn about everything through senses, it is difficult to acknowledge that there are things non-dimensional, non-material which are as real as this chair you are sitting in. In fact they are even more real, because they do not corrupt and pass away as material things do. The greatest of all those immaterial and real beings is God. Since all other beings depend on God, a metaphysician says that God is being itself and He is the only being in the truest sense of the word.

Realism and Idealism

Even though we have just set off, we are already immersed into advanced metaphysics. There are a few notions that require further explanation. Before we move on, however, we need to establish one pre-philosophical issue which is crucial for admitting any of Aquinas’s arguments in metaphysics. It is called moderate realism.

Moderate realism is a cognitive attitude which a thinker adopts before beginning any philosophy. This may sound complicated, so let’s try to explain it step by step. First we need to agree that there is an “I” that is the subject of cognition. When you are reading this text you are the “I”—the subject of the activity of reading. But there is also something external to you – the text you are reading, or the chair in which you are sitting or a bird outside the window. If you find this distinction obvious, you are right. It should be obvious. But it is not obvious for those who have been exposed to philosophy. In fact some philosophers (especially in modernity) claimed that we do not really know if there is that something external to our mind. Perhaps it exists only in our mind. If this was the case our mind and what it contains would be the only being. We said before that what exists in the mind only is not real. But if all what is existed only in the mind, how would you call the entirety of being? Does it mean that there is no reality at all?

Those who assume that everything exists only in mind are called idealists. For them the real (outer) being does not exist (or we cannot know whether it exists or not)—all of what exists is just an idea in the mind. But those who recognize the existence of things outside of their minds know them somehow. This means that those things must somehow enter their minds and stay there in the form of ideas. Your neighbor’s chairs are a good example. When you saw them for the first time you learnt about them through senses (you saw, touched, maybe smelled them). By means of abstraction your mind built an independent idea of the chair. So what you experienced in the outward reality entered your mind as an independent idea. This is how all human cognition works—we derive ideas of things from reality. It happens through our sensual contact with those things. Idealists would say that those things do not exist outside, because either we have them imprinted in our minds from the very beginning or they were produced in our minds through intuition or enlightenment. Realists, like Aquinas and probably every non-philosopher, acknowledge the existence of the objective reality of things outside of the mind and the fact that the human mind learns about those things by contact with them through the senses and an intellectual operation of abstraction. Idealists, in contrast, claim that everything is just an idea in our minds.

There is, however, the third position, called extreme realism. This one claims that the ideas independent from the human mind are the only real beings. This was the position of the ancient philosopher Plato (Aristotle’s mentor and teacher).

To understand Plato’s position we need to adopt his perspective of inquiry. Imagine that you are tired with all this visible reality, with all its shortcomings such as corruption, changes, pain and suffering of the body, weakness, death, etc. You start seeking for an ideal world, another realm, where everything is just perfect, eternal, unchangeable, incorruptible, etc. Plato identified this realm with the world of ideas such as mathematical beings. Was there a time when “triangle” didn’t exist? Can it be corrupted by time, by influence of earthly factors such as wind, water or sun? Is there anything missing in “triangle”? To all these questions the answer is “no”. Plato believed that ideas are perfect and therefore they are real. Our realm of material beings is just a weak, imperfect reflection of that ultimate reality of ideas. Consequently ideas (not only mathematical) are real and constitute some perfect world outside of our minds. Our world of material beings is not real; the ideal world is. We see that Aristotle and Aquinas adopt a medium position between the idealists and extreme realists. This is why their position is called moderate realism. Still, it is “more realism than moderate” because, unlike idealism, it adopts the real existence of things outside of the mind. As we said, every person adopts one of these three cognitive positions even before he or she starts any philosophy. In fact, all philosophical inquiry is determined by this pre-philosophical or even pre-reflective choice. To understand Aquinas and acknowledge his metaphysical solutions one needs to be a moderate realist.

Nominalism vs. Realism

The problem of moderate realism comes close to another big choice that is directly relevant to the problem of biological evolution. Think about words such as “horse”, “dog,” or “car”. Each of them may designate a particular thing or a species (a class) of objects. For example, we say “a car” when we mean some car. We say “the car” when we mean this particular car. But we can also say “car” to designate all objects which deserve the name of a car, that is, the objects among which each one displays the essential features of a car. As we said, our mind creates an abstract notion of a car which we call a species or a universal. A car is a particular object that matches the universal notion of a car. Cars are obviously different and there aren’t two identical cars. Yet, somehow we know what a car is and what it is not.

In medieval Europe the question arose whether those universal notions exist in our minds only or in the actual things too. In medieval times they did not know cars, so let’s resort to another example, a horse. Is it that the general idea of a horse that we have in our mind exists only in our mind and in reality there are only individuals, i.e., separate units of horses? If this were the case our mind would call a horse everything that has horse features but there wouldn’t be anything like horse itself (or “horseness”) in any of those individual animals. Owing to the fact that the idea of a horse is reduced here to the name alone this position is called “nominalism” (from Latin nomen—name). According to nominalists, horse is just the name we use for a class of objects that display horselike features, but there is nothing like horse (in the sense of species – “horseness”) in an individual horse. According to nominalism, horseness does not exist. Thus the name of the species, like horse, is just an organizing name for a class of features. The same applies to any other species – car is just a name that applies to individual objects that bear carlike characteristics. We cannot speak about a universal car unless we mean just a definition, but not the nature or the species of a car. Consequently nominalism reduces universal concepts to individuals – there is nothing like universal beings in reality, these are just concepts in our minds.

Nominalism started in an opposition to the more classic and much older position that we already introduced as realism. In this context, however, our moderate realism gains a deeper and more important meaning. According to moderate realism an abstract idea of a car or a horse exists actually in every individual car or horse. The universal horse does exist—not, as  Plato thought, in some other realm (extreme realism), but in every individual horse. When you see an animal and recognize a horse it is because there is the universal horseness in this particular animal. The correct understanding of this Aristotelian-Thomistic claim is absolutely crucial for understanding the rest of classical metaphysics as well as the problems of theistic evolution.

Let’s go over it again. When you look at a horse you do not see a horse, because your senses do not really perceive a horse. The senses perceive horselike features – the color, the shape, the smell, the sounds – all what typically belongs to a horse. Our human mind has the ability to abstract from these multiple characteristics a unified and universal notion of a horse. Thus, even though every horse is different we can still recognize a horse and distinguish it from anything that is not a horse. Thus we build a general notion that remains in our mind (memory). When we see another object of horselike features our mind associates it with the idea of a horse and thus we can recognize a horse in an animal that we have never seen before. The grand claim of the moderate realism is that the universal horse, or we should rather say – a horse nature, is actually present in every individual horse. In fact it is not our mind that builds the notion of a horse. The horseness exists there in each particular horse and our mind discovers it rather than creates. And the same horse nature exists in each horse. This is precisely why we are able to recognize a horse as a horse even if we haven’t seen this particular horse before. If nominalists were right, how could it happen? Every single feature of a new horse we see is slightly different from a feature of a horse we had seen. Hence, if horse (understood as a horse nature) did not exist in every horse we could not recognize a horse. In terms of moderate realism we can explain our ability of classifying objects thanks to the fact that we recognize the common nature existing in them. Let’s repeat: Moderate realism is the cornerstone of all Aristotelian-Thomistic philosophy. Without adopting it one cannot fully embrace Thomistic arguments. Of course, the debate which one is true – nominalism or realism has had a long and exuberant history. Our goal here is not to convince the Reader of the trueness of Thomistic realism. This would require another good size book. We just indicate its importance. It is a gate. One cannot move on in this debate without accepting moderate realism.

Substance, Nature, and Accidents

When discussing moderate realism we already referred to a notion of nature or substance. We are familiar with these words from daily life. By nature we usually understand environment or surrounding biology. By substance we understand things like sugar, water or some other liquid. We use the word “substance” to call a thing of unknown properties. The metaphysical understanding of “substance” and “nature” is somewhat different. We need to forget about the customary use of these terms and activate our abstract thinking. Substance comes from Latin sub-sistere, which means roughly “to stand underneath”. Every actual being is some substance. Therefore, there is something sitting underneath everything and this is the substance itself.

To make it clearer let’s take any object, like a pen. Every object is something and has something. A pen is a pen, but it has a color, temperature, particular shape, material of which it is made. The same applies to any other object – a horse is a horse and it has features such as brown or black hair, thick bones, longer or shorter tail, mane, etc. Substance is precisely what the thing is whereas what it has (the features) are called accidents. They are accidents because they just happen to be this way but could be different. For example, this car is grey, but if it were black or red it would be still a car. The substance of the car is car (or “carness”) whereas the accidents are its color, model, age etc. What stands underneath (sub-sistit) is the invisible substance of the car (carness) whereas what sits on the top are the visible features, that is, the accidents. Changing the accidents does not change the substance, but changing the substance must change the accidents. It follows that beings which are non-material (spirits) do not have accidents, because accidents come with matter. Spirits are pure substances. Each of them simply is.

Nature is just a substance taken according to the mode of its operation. For example, it belongs to the nature of a fox to be smart. We can say that his substance is of a kind of smartness. The substance of a horse and the horse nature is the same in all horses, and the substance of a fox and the nature of a fox is the same in all foxes. But the accidents differ in each individual. Substance is also close to another notion—“essence” or “whatness” (Latin quidditas). Substance stresses an aspect of existence (substance is what exists underneath), whereas essence highlights what a thing is, its individuality and specificity. Even in common language when we say that something is essential for us we mean that we need this and not something different. Also, when we say that justice is the essence of law we mean that justice is most proper to law, that law wouldn’t be itself if it wasn’t just. Similarly in metaphysics, when we say that the essence of a man is humanness we mean that human nature—humanity —is what makes a man to be a man, and “horseness” is what makes a horse to be a horse. Consequently, we can say that substance is something separated from everything else, something contained in itself, something specified and unified.

The Hierarchy of Substances

Another grand claim of Aristotelian-Thomistic metaphysics is that substances constitute a hierarchy. In other words, even though everything that exists is a substance in some sense there are some things that constitute substance in a deeper and truer sense than the other. The hierarchy in the descending order looks like this:

Spirits (angels)

The only true substance is God alone. He is one and indivisible in the highest degree, He is the most self-contained, most specified and simply the most “is”. Every other substance is just a substance by participation in God. The highest created substances are the angels. Their specification (and therefore essentiality) is much greater than that of any material being. Below angels there are humans who have the subsistent soul. This means that human soul may exist without matter though naturally it exists with the body (the material component of a human being). The subsistent soul makes humans more specific and unified than any other material being. Below humans there are animals and plants. Below plants there are non-living physical objects such as compounds and elements. In fact neither of them should be called substance because they do not constitute unity. They are not distinct; they are not specified or self-contained. Hence, in metaphysical terms water is not substance, it is merely a compound. If we call it substance we do it in a very weak way and only by analogy to the true substances. Elements and compounds are in a way a contradiction of substance. Similarly, artifacts, though sometimes quite complicated and very much organized (e.g., computers, cars), are not substances but ensembles of parts, compounds and elements.


We used before the examples of a car and a pen to speak about substance. But we also said that artifacts are not true substances. Indeed, they are very much unlike substances. Is there a contradiction in what we say? To understand why there is no contradiction we need to refer to another tool in metaphysics, which is analogy. The theory of analogy is a whole separate discipline which would require a good-sized book to be fully explained. In our opinion the main reason why some intellectuals, including many philosophers, reject classical metaphysics is that they do not understand the analogous character of metaphysical concepts.

We can explain analogy by contrasting it with what is univocal and what is equivocal. For example, when we say “a table” we do it univocally, which means there is no ambiguity in what we say. But when we say “a bat” we can mean an animal or a kind of club. When we say “a bolt” we can mean a certain kind of metal object or a streak of light that appears in the sky during storms. Similarly, the word “chapter” may refer to a chapter in a book or to a human assembly. These words are equivocal because they refer to two completely different things. The analogous is something between the univocal and the equivocal. The analogous term is predicated about (i.e. applies to) two or more different things because they have something in common. In the case of substance, we predicate it because every substance constitutes a unity, is specified, integral and distinctive. But the way in which things fulfill the requirements of being a substance are very different. Water, as we said, is not a substance but a compound. Yet, in some sense it is distinctive from other compounds and for this reason, in an analogous sense, it is called a substance. And the same analogous mode of predication (i.e. applying terms) belongs to all typically metaphysical notions such as act and potency, form and matter, substance and accidents, etc. Thomas Aquinas says that all our talk about God is analogous. This means we can make true and unequivocal statements about God, but they do not mean the same what we mean when speaking about creatures. God is beyond our human language. We explain his mystery only by analogy.

Substance and Existence

We mentioned before that substance is essence with an emphasis on its existence. Substance is that what exists under the accidents. However, we can think of many different substances which do not exist. If you think of your own elephant it is quite probable that you think of a substance that does not exist. It is therefore possible to distinguish two things: the substance (the nature or the essence) of a thing on the one hand, and its existence on the other. (Saying “actual existence” is redundant in this context because existence itself implies actuality. As we said, potential existence is not existence at all). But we should not think of existence as something attached to a substance the way covers are attached to books. Existence pervades substance, just as sunlight pervades air. Existence is something most proper to substance, is an act of substance which makes it to be. We can say that existence is not what substance has but what it does.

Act and Potency

We have already used a few times the word “actual”. In our common language this term signifies something up-to-date. We say the software is actual, or the database has been actualized. In the metaphysical sense, actual means realized, accomplished, finished and perfect. In common language we also use a term potential. By potency we usually mean “a power”, an ability to do something. Again, in a metaphysical sense it is slightly different. If something is potential (or “in potency”) it means that it is still-to-be-realized, that it is not yet accomplished or finished.

Let’s refer to an example. When a construction company starts building a house we can say there is a house in potency. There is a construction site prepared for raising the building; there are workers, tools and materials needed to build a house. But there is no actual house, the house is only in potency—it exists only potentially in the materials, the power of the workers and the mind of the architect. Once the house is built, we say that in metaphysical terms it passed from potency to act. The house has become actual, i.e., it now actually exists. Still there is a lot of potency in the actual house. For example, it can be furnished, remodeled or even torn down. If you think about it you realize that every creature has “some amount” of act and some amount of potency. Everything created is stretched between potency and act. At the extremes there is a pure potency and a pure act. Different beings have different “amounts” of potency and act. Some are more actualized than others. For example, the angels have more actuality than beings with bodies have, because they do not corrupt with lapse of time. But they may be annihilated by God at any moment. This means they are in potency to non-existence. The only pure act is God himself. His substance or nature identifies with his existence. God is a pure being; his nature is to exist and this is why God can neither cease to exist nor change in any way. This is also why God is absolutely perfect—in him everything is realized, which means everything is accomplished.

Form and Matter

We said that everything created is stretched between a pure act which is God alone and a pure potency. That pure potency is called matter. Matter in metaphysics has a different meaning than in the common language. In daily usage by matter we mean a material – something that serves to make different things. A cloth or a brick is a matter used to make clothes or build houses. But in metaphysics matter is something that underlies all material being. It is something that makes a thing become a material individual, but itself is not determined in any way.

To better understand what matter is we need to introduce still one more concept, that is, the concept of a form. Again, in common language we use the word “form” typically to signify a shape of a thing. We say, a cap has a form of a cone or a plate has a form of a circle. We also say that we form something into something. This popular use of the word is not completely different from what we understand by form in metaphysics. But again, to understand what we mean in metaphysics we need to think in an abstract way. Form, in metaphysical terms, is all specification of a thing. It is everything that characterizes a thing. We can say form is what makes a thing what it is.

Think, for example, of a dog. The form of a dog is everything that we can say about it. In this sense form is something that in-forms us about a thing. In fact the very word “to inform” means to put a form of a thing into our mind. Form is therefore all knowledge that we can derive from a particular thing to make it known to us. Thus the form of a dog is everything that a dog has. For example, it has four limbs, two ears, one head, a tail (even if rudimentary), a dog type of respiratory system, of blood system, of skin, pelage, etc. All of this constitutes the form of a dog. If a dog didn’t have a dog form it wouldn’t be a dog. In contrast, matter is something that is in-formed (shaped) by the form. The form of a dog without matter could not constitute a dog substance. Matter is the underlying, completely undetermined potency which is actualized by the form. Form is like an act of a dog, whereas matter is what makes it to be in potency to different things. Matter is something that is a pure potency. But as we said, the form is what in-forms our minds. We understand only the form of a thing because this is the whole and the only determination and specification of a thing. Hence the paradox—we cannot really know what matter is, because matter is precisely that which has nothing knowable in itself. It is a negation of any knowledge or understanding. It is “perfectly” undetermined and unspecified. This is why when we say we understand what matter is, we speak truly only when we understand that we cannot understand anything about it. But if it is so, how do we know it exists? Well, it does not exist separately from the physical objects. By itself it is just an intellectual construct. It exists only in combination with a form. If there were no matter all beings would be just formal, that is, immaterial. We know, however, that bodies are material, therefore there must be something that makes the form material, and this is the underlying matter.

We should additionally notice that matter is a general concept that—together with form—explains the existence of a material being. In a general sense it is called prime matter (Latin materia prima). However, we can also think of matter which exists in an individual material being. Matter which exists in an actual being is somehow specified and disposed. We call it designated matter (Latin materia designata). In the discussion about evolution it is important to know that designated matter exists only in the combination with the form in the actual being. We cannot see the form as something attached to designated matter. Designated matter doesn’t exist separately from the form. In an actual being the distinction between the form and designated matter is only in thought; there is not a real existence of the two as if they were parts of one. Rather matter is a potency that is actualized by the form. A misunderstanding of this detail has led some Thomists to produce false metaphysical arguments in favor of theistic evolution.

Substantial Form, Accidental Form, and Individual Form

We explained before that substance or essence is what makes the thing what it is and accidents are what it has. Both substance and accidents constitute some determination or specification of being. For example, a horse embodies the substance of a horse (horseness) and it also has accidents typical for horses (horse-like features). But we also said that form is what gives a thing all intelligible content. Whatever we can know about a thing comes from its form. Accordingly we can speak about the substantial form and the accidental form. The substantial form is the one that determines the substance of a thing, namely what it is regardless of its accidents. The accidental form is the one that makes the thing the way it is in this particular moment and circumstances. Accidental form informs us about what the substance has. Often, “substantial form” is used interchangeably with the “substance” or “essence” of a thing and “accidental form” means roughly the same as the accidents of the being.

Now, if we think about an individual being we can say that it has its own individual form. This form comprises the individual substance and the accidents of this particular being. The individual form is the one that actualizes (informs) designated matter. But this same being has the substantial form which is the same in all beings sharing the same nature or species. This is why we can oppose the individual form and the substance of a thing. Substance may be the same for many things (e.g., many horses have the same substance of the horse) but the individual form is particular to just one thing (e.g., this one horse). Changing the accidents leads to changing the individual form, but not the substance. For example, we can trim the main of a horse. It will change the individual form of this particular horse, but it will not change the substance (or substantial form) of this horse. Neither will it change anything in the substance (or species) of any other horse. The “horseness” which exists in every horse is not affected in any way by an accidental change in an individual of the horse species.

The Structure of Being in Classical Metaphysics

As a summary of our discussion regarding the structure of being we present the following schemes:


One of the basic principles of metaphysics says that everything has a cause, a reason of its existence and/or operation. If you think about it, you realize that this principle is not just some abstract idea in the narrow field of metaphysics. This principle applies outside of philosophical contexts. In fact it is a common-sense principle that we see wherever we look in physics, biology, astronomy, or our daily life. Everything is caused by something else. In metaphysics, however, we can trace the chain of causes and effects up to its ultimate source which is the highest being, the Absolute. God is the only being which is a cause but itself uncaused. We can say that He is the cause of himself. From him everything else receives its cause, either immediately or by means of mediation through creatures.

Types of Causality

When we speak about God being an immediate cause we mean that He causes something directly without using anything else. Similarly, we say that a man can do something directly, as when a man picks up a nail from a bag, or indirectly (i.e., through the mediation of another being), as when a man uses a hammer to drive a nail into wood. In the latter case the primary or first cause is the man whereas the secondary cause is the hammer. We can therefore say that both the hammer knocks the nail and that the man knocks the nail. We can also say that a carpenter cuts wood or that a saw cuts wood, not by itself but by the power of the carpenter who works as the first cause.

There is also a particular type of secondary cause which is called instrumental. Let’s refer to another example. A piece of chalk can be left on a table. Imagine that wind blows so strongly through the classroom that the chalk is moved on the surface of the table and marks it with some white lines. In this case the wind is the primary cause whereas the chalk serves as a secondary cause in drawing lines on the table. But then a teacher comes in, takes the chalk and writes on the blackboard. Again, the teacher is the primary cause and the chalk is the secondary cause. However, in the latter case the effect, which is an intelligible text written on the board, exceeds the natural power of the secondary cause, i.e., chalk. It belongs to the nature of a chalk to leave marks on a surface; however, it is beyond the nature of chalk to write a poem or a mathematical equation. Whenever the secondary cause is induced by the primary cause to act beyond its natural capacity, we call the secondary cause an instrumental cause. Thus, the chalk in the first example was just a regular secondary cause but in the second example it became an instrumental cause.

To summarize: Every chain of causes and effects has the first cause and the secondary causes. If there is no chain, but some cause acts directly upon the last effect, we call it a direct or immediate causality. Christians confess that God works in both ways: directly when He does something without using other creatures, and indirectly when He uses creatures to bring about intended effects. A good example of direct divine causality is the creation of things. There cannot be any secondary cause in creation, because creation is emanation of being out of nothing. In creation the beginning is nothingness, the end is something. But any secondary cause is already something that acts in some manner. An action of any created being is somehow determined. For example, a hammer can knock things, a chalk can leave marks, a dog can bark or chase a rabbit etc. But no created being acts towards producing the very existence of a thing. This is why creation can be accomplished only by God alone.

Still, God uses creatures as natural or supernatural secondary causes. For example, when God uses natural phenomena, such as thunder, to incline someone to do something, we can say that the thunder becomes a secondary natural cause of this effect (for example, a conversion of a sinner who decided to change his life due to the fear incited by a sudden thunder). When God uses angels or souls to accomplish something in the world they become secondary supernatural causes. For example, the soul of a deceased person, shown to a man to make him pray for her salvation, becomes a supernatural secondary cause of the prayer of the man. In creation there is neither natural nor supernatural secondary cause, whether regular or instrumental.

The Four Causes

There are four types of cause described in classic metaphysics. Every material being must have all four of them; otherwise it cannot exist. To explain a being, or to find the reason of its existence, means to find its four causes. Like all other metaphysical concepts, the four causes are also analogous. To explain them we will refer to an example of daily life and then try to extrapolate it (abstract it) into metaphysics.

Imagine a sculptor working on a sculpture, let’s say, Michelangelo working on his Moses. To curve Moses, Michelangelo needs material, in this case marble, needs his own hands or his students’, and a chisel. He also needs to have an idea in his mind of what he wants to curve. All of these are causes of the statue of Moses. Marble is the material cause—if there is no marble there is no statue. Michelangelo’s hands are the efficient cause. The chisel is also the efficient cause, but secondary. The formal cause is the form of the marble, in this case the form of Moses, based on what we know of (or how we imagine) the historical person Moses. And there is also the final cause, which in this case is the intention of the sculptor: the idea of Moses that Michelangelo has in his mind.

Now let’s translate this example into metaphysical terms. Material cause is matter (taken in the metaphysical sense). Immaterial beings, such as angels, do not have the material cause. The efficient cause is something that causes something to become. We can easily imagine the efficient cause because this is the type of cause which different natural sciences typically identify within their subject matter. The efficient cause of planetary movements is gravity. The efficient cause of a car going on the road is its engine, the efficient cause of the heat coming from the fireplace is fire, and so on. The efficient cause is the one that makes things. The formal cause is harder to grasp, because it is rarely an object of study of any natural science and requires more abstract thinking. The formal cause is what makes a thing what it is. Generally speaking, the formal cause is the form of a thing because the form is what makes the thing what it is. The final cause is something that makes a thing to become or tend toward a certain goal. In our example, the idea of Moses in the mind of Michelangelo drives him to produce the figure of this particular shape. We can imagine the final cause as a kind of magnet attracting things to itself and thus making them this way or another way or causing them to act in a particular way. In contrast, the efficient cause is like a pusher that pushes things toward their goals.

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