Reading Aristotle: Physics 2.3: The Four Causes

In Chapter One of the second book of the Physics, Aristotle discussed how natural objects are distinct from artificial objects by virtue of intrinsic natures. In Chapter Two, he distinguished between the sciences of physics, mathematics, and metaphysics, concluding that physics as a science studies both the form and matter of things. In Chapter Three, he explores causation:

“Now that we have established these distinctions, we must proceed to consider causes, their character and number. Knowledge is the object of our inquiry, and men do not think they know a thing till they have grasped the ‘why’ of it (which is to grasp its primary cause). So clearly we too must do this as regards both coming to be and passing away and every kind of physical change, in order that, knowing their principles, we may try to refer to these principles each of our problems” (Physics 2.3, 194b16-23) [1].

It will be helpful here to recall and keep in mind what Aristotle’s overall project in the Physics is: physics, as Aristotle sees it, is the science of nature, and nature is the principle of motion/change in things; so physics is always going to study change in physical reality. In Book One, Aristotle established what the underlying principles of change were: namely form, substratum (or matter), and privation. These are the principles of change, what change consists of primarily; but there is still the need to fully explain how/why change occurs. In order to fully understand the process of change, then, we have to know its causes.

What Aristotle points out at the start of this present chapter is quite profound. First, he states that the object of scientific inquiry is not use but knowledge. As Aquinas puts it, “The business of studying nature is not ordered to operation, but to science [2].Which is not to say that technological innovation as a result of scientific discovery is a bad thing; but rather that, especially since the birth of the modern era, we often lose sight of the sublime beauty of the pursuit of knowledge for knowledge’s sake. Philosophy and science are both driven, at heart, by wonder; and wonder is intrinsically a desire for knowledge. There is a vast difference between gazing at the stars in order to discover what use might be made of them, how their resources and materials might be garnered and manipulated — and gazing at the stars in awe of their own splendor, with a desire to know them just because of what they are.

Second, he states that knowledge fundamentally consists of grasping the “why” of something. Not just the the descriptive “what”, or the mechanistic “how”, but the explanatory why. And this “why” is discovered through a thing’s “primary cause”. Today, we use the term “cause” in a somewhat limited manner. For instance, if a builder constructs a house, we would normally just consider the builder himself as the “cause”, rather than, say, the wood he uses, or the blueprint he follows. But for Aristotle, “cause” has a broader and richer implication, connoting a full explanation of a thing. The science of nature, then, must study physical change in order to discover its causes and have a complete understanding of the principles of nature.

“In one sense, then, (1) that out of which a thing comes to be and which persists, is called ’cause’, e. g. the bronze of the statue, the silver of the bowl, and the genera of which the bronze and the silver are species” (2.3, 194b23-26) [3].

The first type of cause that is considered is the material cause, the “that out of which” a thing becomes and is made. Wood or stone is the material cause of a house, since it is the material out of which a house is made and of which it consists. Similarly, bronze is the material cause of a statue, silver of a silver bowl, various metals of a car, paint of a painting, rubber of a rubber ball, etc. The material cause seems to be a necessary but not sufficient factor in explaining a thing. Without bronze or marble or some other material you couldn’t have the statue; but at the same time, the bronze or marble alone won’t give you a statue.

Aristotle notes two functions of the material cause: it is that out of which a thing comes to be, and it is that “which persists”. There are different ways we could take this latter point. First, for Aristotle, matter is what underlies a substantial change (a change from one substance to a different substance). For instance, if I had a wooden house, and then tore it down, took the same wood and built a wooden boat, the wood itself does not change, but the substantial form which instantiates it does. First, the wood makes up a house; then, the wood makes up a boat. It is the same wood throughout the whole process, and indeed it is the wood which underlies the change itself and even allows for the change to happen at all. The form changes, but the matter “persists”.

A second way we could take it, however, is in relation to privation. Remember that Aristotle in Book One concluded that privation is one of the principles of change, along with matter/substratum and form. If a man who doesn’t know how to play any musical instruments learns how to do so, he changes from “non-musical” to “musical”. The former is the privation, the latter is the form, and the man himself is the subject/substratum which underlies the change, because it is in him that the attributes inhere. When the form arises, the privation necessarily is destroyed, or ceases to be. A man could not be both “musical” and “non-musical” at the same time. So the privation does not persist in the substance that becomes. But the matter does. In other words, just because a form arises, the matter is not necessarily destroyed. On the contrary, the form must arise in the matter, and the new substance includes the form and the matter. So the matter “persists” in the sense that it still exists in the substance along with the new form [4].

He continues:

“In another sense (2) the form or the archetype, i. e. the statement of the essence, and its genera, are called ’causes’ (e. g. of the octave the relation of 2: 1, and generally number), and the parts in the definition” (194b26-28) [5].

This is the formal cause, the form or essence or “whatness” of a thing, its archetype or blueprint or “shape”. Above we said that bronze is necessary but not sufficient to constitute a statue. Instead, the bronze needs to be given the form of a statue in order to be a statue. Wood itself is not equivalent to a house; it needs to be built according to the blueprint/design of a house.

The formal cause is captured in a thing’s definition, or “the statement of the essence, and its genera”. So “rational animal” is the definition of man, where “rational” is our essential feature and “animal” is its genus. Aristotle gives the example of an octave ( a series of eight musical notes, the extremes of which are two notes whose higher extreme doubles the vibration frequency of the lower): the form of the octave, he says, is the relation 2:1. This uniquely captures the idea of form. The air vibrations which make up a particular sound are like its matter, while the frequency and proportion of the vibrations are its form. Suppose, for instance, a singer opens her mouth to sing the note “C”. The air itself which she is about to release from her lungs does not yet have any determinate sound; but it has the potential to be shaped into almost sound which the singer can give to it. The air itself has the potential to be shaped into any note, but of itself it is none of them. Only when the singer herself releases the note, giving it a certain vibration frequency, does it gain a determinate form and become an actual sound/note.

An octave specifically is a harmony with the relation 2:1, and so its form, Aquinas explains in his commentary, is the “proportion of double”, i.e. what makes an octave an octave is the ratio between its first and last notes, which is double. But a proportion of double is, of course, contained within the genus of “number” or multiplicity, and so this genus will be included in its definition and hence gains by association the position of formal cause. So, as Aquinas says: “All of the parts which are placed in the definition are reduced to this mode of cause” [6]. Using an easier example, “animality” can be considered as part of the formal cause of man,

The third kind of cause:

“Again (3) the primary source of the change or coming to rest; e. g. the man who gave advice is a cause, the father is cause of the child, and generally what makes of what is made and what causes change of what is changed” (194b29-32) [7].

This is the efficient cause, which is most commonly known just as “cause” today. The efficient cause is also known as an “agent” cause, because it is the primary agent doing or driving or powering the change. It is the source of the activity. The artist is the efficient cause of the statue; the singer’s lungs are the efficient cause of the song. It is that which is responsible for bringing something about, or “that from which there is a beginning of motion or rest” [8].

“Again (4) in the sense of end or ‘that for the sake of which’ a thing is done, e. g. health is the cause of walking about. (‘Why is he walking about?’ we say. ‘To be healthy’, and, having said that, we think we have assigned the cause.) The same is true also of all the intermediate steps which are brought about through the action of something else as means toward an end, e. g. reduction of flesh, purging, drugs, or surgical instruments are means towards health. All these things are ‘for the sake of’ the end, though they differ from one another in that some are activities, others instruments. This then perhaps exhausts the number of ways in which the term ’cause’ is used” (194b33-195a3) [9].

We explored this final type of cause more in depth in the previous chapter. It is perhaps the most challenged notion of causation, but for Aristotle and especially Aquinas, it was the most fundamental and the most profound. Consider Aristotle’s revealing example of a person walking: if you were to ask someone why they were walking, and they responded “because my legs are moving”, or “because I am made of a complex assortment of bone, muscle, ligament, tissue, etc. that enables my legs to contract and relax in such a fashion that they propel my body forward”, you would find neither of these a satisfactory answer. Our word “because” illustrates the causal nature of ends. The person is walking because he desires health; his desire for health really does cause him to walk, directing the formal, material, and efficient causes. Of course, modern thinkers who don’t rule out final causation altogether will insist that it can only exist in the realm of conscious, rational agents such as humans. But Aristotle and Aquinas argue extensively that final causation is very much an intrinsic aspect of natural beings just as much as in rational ones.

“As the word has several senses, it follows that there are several causes of the same thing (not merely in virtue of a concomitant attribute, e. g. both the art of the sculptor and the bronze are causes of the statue. These are causes of the statue qua statue, not in virtue of anything else that it may be — only not in the same way, the one being the material cause, the other the cause whence the motion comes” (195a3-8) [10].

Since there are all these different types of causes, but all are really causes, it follows that these causes are all per se causes of the same thing, and not merely per accidens causes. In other words, in explaining the reality of the statue coming to be, we cannot just point to one of the types of causes and say “that is the only real cause of the statue, the other types are just accidental causes”. The artist is not incidental to the reality of the statue, nor is his intention to build the statue, nor is the design of the statue, nor is the material from which he builds it. All of these are essential to explaining the statue’s reality. Neither are the causes reducible to each other: they are all really causes, and they all are designated by the term “cause”, but that does not mean that they are all really the same or equivalent. The material cause is distinct from the formal cause is distinct from the efficient cause is distinct from the final cause, but all are still causes, and causes of the same statue.

“Some things cause each other reciprocally, e. g. hard work causes fitness and vice versa, but again not in the same way, but the one as end, the other as the origin of change. Further the same thing is the cause of contrary results. For that by which its presence brings about one result is sometimes blamed for bringing about the contrary by its absence. Thus we ascribe the wreck of a ship to the absence of the pilot whose presence was the cause of its safety” (195a9-14) [11].

Because there are multiple causes, the causes can be discovered to have interesting relationships with each other. In particular, it seems that some causes exist in a reciprocal relationship. For instance, hard work is the cause of fitness in that working hard brings out fitness; hence hard work is the efficient cause of fitness. But fitness itself is at the same time the cause of hard work, in that one works hard for the sake of bringing about fitness (“Why are you working hard?” “Because I want to be fit”); hence fitness is the final cause of working hard. So the efficient and final causes work reciprocally.

In addition, one thing can sometimes be the cause of contraries, although in different senses. Safety of a ship is contrary to its wrecking. The pilot’s presence on the ship is the cause of its safety; but his absence is the cause of its wrecking, in that his absence really is a contributing factor to the ship’s misfortunes. But, again, the same pilot is the cause of contraries in different senses.

“All the causes now mentioned fall into four familiar divisions. The letters are the causes of syllables, the material of artificial products, fire &c., of bodies, the parts of the whole, and the premisses of the conclusion, in the sense of ‘that from which’. Of these pairs the one set are causes in the sense of substratum, e. g. the parts, the other set in the sense of essence — the whole and the combination and the form. But the seed and the doctor and the adviser, and generally the maker, are all sources whence the change or stationariness originates, while the others are causes in the sense of the end or the good of the rest; for ‘that for the sake of which’ means what is best and the end of the things that lead up to it. (Whether we say the ‘good itself’ or the ‘apparent good’ makes no difference.) Such then is the number and nature of the kinds of cause” (195a15-27) [12].

So, he concludes, there are four types of causes. But even here he seems to at least implicitly arrange the four causes into two broader categories of reciprocal relationships. In the first part of the passage, he lists a number of examples of causes which relate matter to form: letters to syllables, material to products, elements to bodies, parts to wholes, premises to conclusions. In each of these relations, the first term is the material cause, the second is the formal cause. A whole is made up of parts, but what it is is the whole.

In the second part of the passage, he similarly relates efficient causation to final causation. The efficient cause is the source whence a motion originates, and the final cause is to which or for which it originates. (For more on his comment about the final cause being the “last and best” end, see the post on the previous chapter).

(Note: it might seem that Aristotle is being redundant here by repeating the four causes. But I think what he’s doing is this: at the start of the chapter, he explained that the word “cause” is used semantically with four different meanings/sense. Now he is arguing that the semantic uses of the word reflect a metaphysical reality. Not only do we use the word cause in these different senses, but there are actually these different types of causes, and this is how they operate).

The rest of Chapter Three we will cover more briefly, without quoting line by line.

He has so far given the types or kinds or species of causes; but there are also various “modes” of each type of cause. These, Aristotle says, are numerous, but can be reduced to a few categories/divisions.

The first mode of causation is the distinction between prior/universal causes to posterior/particular causes. For example, a doctor is a cause of health. But a doctor is just a particular type of expert or professional. “Expert” then is a more universal cause.

A second mode is the distinction between proper and incidental (or per se and per accidens) causes. A sculptor is the cause of a statue. But any sculptor is also a human. Being a man and being a sculptor are accidentally or incidentally joined in the person who is creating the statue. In other words, it is not an essential quality to all humans to be sculptors. So a person who is carving a statue is doing so qua human incidentally, but qua sculptor properly or essentially.

A third mode is the distinction between actual and potential causes. A cause can be actually causing something, or it can just have the potential to cause something.

These distinction which we make in the causes can similarly be made in the effects or the things being caused. Just as a doctor is the particular cause and an expert the universal cause of health, so also is a statue the particular effect of a sculptor and “a piece of art” is the universal effect.

Finally, a cause can be considered either as a simple or a complex expression. We can say “David carved the statue”, or “The sculptor carved the statue”, or “David the sculptor carved the statue”. All of these may seem to be just trivial, semantic distinctions, but Aristotle is trying to be as precise as possible in figuring out the nature of causes. To take just our last example: if we say that David is the cause of the statue, what exactly do we mean? What about David is the cause of the statue? Making these careful distinctions helps figure out what exactly a cause is and how it explains the reality which we are invoking it to explain.

To finish Chapter Three, Aristotle explores some of the implications of these distinctions:

He notes that causes that are particular and actual (rather than universal and potential) “exist and cease to exist simultaneously with their effect, e. g. this healing person with this being-healed person” (195b17-19) [13]. But this is not always the case with potential causes. A housebuilder and a house do not cease to exist at the same time.

He also notes that in searching for the causes of things we ought to search for the first cause, that which explains the other causes in a series. This is the significance of the “particular/universal” distinction above. For example, a man builds because he is a builder. Being a builder is a cause of him building. But he is a builder “in virtue of his art of building” (195b23-24) [14]. So “the art of building” is a cause of him being a builder; it is what makes him a builder. “The art of building” is the first cause in this series and it is the more universal cause.

Finally, he notes that causes and effects should be related proportionally. A generic effect should be assigned to a generic cause, and a particular effect to a particular cause. To be a potential cause is to have the “power” to bring about a certain effect; while an actual cause must be the cause of some actual effect.

“This must suffice for our account of the number of causes and the modes of causation” (195b29-30) [15].

In this chapter, then, Aristotle first established what the types of causes are, and then the way in which those causes can cause things.

In the next chapter, Aristotle will begin to discuss how chance and spontaneity fit into his understanding of causality.



[1]. McKeon, Richard, editor. The Basic Works of Aristotle. New York: Random House, Inc, 1941.

[2]. Thomas Aquinas. Commentary on Aristotle’s Physics. Books I-II translated by Richard J. Blackwell, Richard J. Spath & W. Edmund Thirlkel Yale U.P., 1963. <>. Lectio 5.176.

[3]. McKeon. Aristotle.

[4]. Aquinas. Commentary. Lectio 5.178.

[5]. McKeon. Aristotle.

[6]. Aquinas. Commentary. Lectio 5.179.

[7]. McKeon. Aristotle.

[8]. Aquinas. Commentary. Lectio 5.180.

[9]. McKeon. Aristotle.

[10]. Ibid.

[11]. Ibid.

[12]. Ibid.

[13]. Ibid.

[14]. Ibid.

[15]. Ibid.

Header Image: Raphael [Public domain], via Wikimedia Commons.





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