Aristotle’s Physics: The Four Causes

How would Aristotle have used computer graphics to depict his ideas about the Four Causes?

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Abstract

Aristotle wrote his Physics ca. 350 BC. Although they appear primitive by our 21st Century standards, they capture the wisdom of the ages. Aristotle, in his time, may have used diagrams when discussing the Four Causes, but all that survives is his prose. The plain text is inadequate for modern understanding so I created some graphics that explain his concepts more clearly to a contemporary audience.

Introduction

Aristotle’s writings date from over 2300 years ago and include many books chock full of wondrous ideas. This Knol presents and interprets the Four Causes (Material, Formal, Efficient, and Final). In each case, we start with a computer graphic that approaches the topic from a “practical engineering viewpoint”. That should give the reader a clear and satisfying concept of what I think Aristotle was getting at. It is what I think Aristotle would say if he was privy to our modern scientific understanding and word usage and had access to computer graphics!
 
I find philosophy hard to understand. As my PhD advisor told me, philosophers make simple things complex, using a language specially created for that purpose! 
 
I attended lectures and read books that touched on things philosophers called the Formal Cause and the Efficient Cause and these terms flew right over my head.
 
Well, it turns out Aristotle himself would not have understood those two terms because he did not use them. To us, a cause is directly and immediately responsible for an effect, but the Greek word for cause “ation” has the broader meaning of explanitory factor.
 
OK, let’s give Aristotle access to modern computer graphics and see where that takes us! For starters we’ll stick to a simple and familiar example, a house and furniture.
 

The Four Causes

 

How do such things as houses and furniture come to be? Aristotle breaks it all down into the Four Causes that modern philosophers call the Material, Formal, Efficient, and Final. The Greek word “aition” is usually translated as “cause” but it also carries a broader meaning, “explanitory factor”. According to Aristotle, the Four Causes can be delineated for anything that comes to be, from natural things such as plants and animals to material things like houses and furniture, and even things like music and art. Indeed, he uses it to explain how diffficulty in moving his bowels causes him to walk in the hope that action will lead to the desired final result!
 
All Aristotle quotes are from the MIT Internet Classics Archive.
 
“All the causes now mentioned fall into four familiar divisions…. (1) that out of which a thing comes to be and which persists, is called [the Material] ’cause’, …(2) the form or the archetype, … are called [the Formal] ’causes’  … (3) the primary source of the change or coming to rest … is [an Efficient] cause, … (4) in the sense of end or ‘that for the sake of which’ a thing is done … is the [Final] cause …”  [Aristotle, Physics, Book II, Part 3]
 

Material Cause

 

The Material Cause is THAT OUT OF WHICH” or THAT FROM WHICH. In the case of a house and furniture, it is the building and woodworking materials such as stone and wood. In that sense the meaning of “material” is quite clear. However, Aristotle states that he intended to use that term for things that are quite immaterial such as the letters of the alphabet or the syllables of speech. 
 
“In one sense, then, (1) that out of which a thing comes to be and which persists, is called [the Material] ’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….”
 
“… The letters are the [Material] 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 [Material] causes in the sense of substratum, e.g. the parts, …” [Aristotle, Physics, Book II, Part 3] 
 

Formal Cause

 

The Formal Cause is THAT INTO WHICH, namely the FORM or PATTERN. In the case of a house and furniture, it is the traditional design or the blueprints and plans that are to be followed to form the building materials into the desired shape and function. When I first heard about the “formal” cause I had no idea what it meant. To me, the word ”formal” is the opposite of “casual”. It is associated with fancy writing and dress and the procedures of august bodies like the Supreme Court.
 
After thinking about it, I like the term. Formal dress entails wearing a particular style of clothing like the tuxedo I had to rent for my wedding. Formal writing, such as a research paper for a professional journal or a legal brief also follows an established style. Aristotle did not use the word “formal” but he applied this type of cause to many things including musical instruments where an octave is formed by the relation of 2:1. That is, three notes of 200Hz, 400Hz and 800Hz are each an octave apart. In modern biology we would call the sequence of codons in DNA the formal cause of the proteins they code for.
“In another sense (2) the form or the archetype, i.e. the statement of the essence, and its genera, are called [the Formal] ’causes’ (e.g. of the octave the relation of 2:1, and generally number), and the parts in the definition.”
 
“… the other set [the Formal cause] in the sense of essence-the whole and the combination and the form….” [Aristotle, Physics, Book II, Part 3]
 
 

Efficient Cause

 

The Efficient Cause is THAT BY WHICH, namely the EFFECTOR or MEANS. In the case of a house and furniture, it is the stonemason, the carpenter and other craftsmen (and women) and factory workers who apply the formal design to the building materials to create the final product. When I first heard about the “efficient” cause I had no idea what it meant. To me, the word ”efficient” is associated with “efficiency experts” who do time and motion studies to improve factory workflow and save money. Aristotle did not use the term efficient” and I do not like it. However, it is the accepted term used by philosophers, so let us get used to it! (Keep in mind that philosophers make simple things complex, using a language specially created for that purpose! )
 
Aristotle says a man who gives advice, or a man who is a father, is the cause of the child. I would actually give the mother who carries the child during the nine months of gestation that distinction!
“Again (3) the primary source of the change or coming to rest; e.g. the man who gave advice is [an Efficient] cause, the father is [Efficient] cause of the child, and generally what makes of what is made and what causes change of what is changed.”
 
“… But the seed and the doctor and the adviser, and generally the maker, are all [Efficient causes] sources whence the change or stationariness originates, …” [Aristotle, Physics, Book II, Part 3]
 
 

Final Cause

 

The Final Cause is THAT FOR THE SAKE OF WHICH” or FINAL RESULT. In the case of a house and furniture, they are built for the sake providing a comfortable place to shelter a family.  Aristotle uss the term “end” and perhaps End Cause would have been better. However, Philosophers use Final Cause and that is the term we are stuck with!
 
Aristotle is much concerned about health and appears to have been quite a walker. Recall that In that sense the meaning of “material” is quite clear. However, Aristotle states that he intended to use that term for things that are quite immaterial such as the letters of the alphabet or the syllables of speech. 
“Again (4) in the sense of end or ‘that for the sake of which’ a thing is done, e.g. health is the [Final] cause of walking about. (‘Why is he walking about?’ we say. ‘To be healthy’, and, having said that, we think we have assigned the [Final] cause.) The same is true also of all the intermediate steps which are brought about through the action of something else as means towards the end, e.g. reduction of flesh, purging, drugs, or surgical instruments are [Final Cause] 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.”
 
“… while the others are [Final] 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.” [Aristotle, Physics, Book II, Part 3]
 

Spontaneity and Chance 

Spontaneity, according to Aristotle, is the broader term for unusual events. Chance is a subset of spontaneity. Both “from spontaneity” and “from chance” may be the Efficient causes of events.
 
 

Spontaneity

Spontaneity (and its subset chance) may be incidental Efficient causes. If a stone happens to fall and strike a man, that is from spontaneity but not from chance if no one capable of moral action was involved with the stone falling. Unusual events due to actions of nature or actions of lower animals incapable of moral action are said to be spontaneous but not by chance.
 
Nature causes changes in itself much as a doctor doctors himself. However, acording to Aristotle, nature does not work for the sake of some end or purpose, but of necessity! Things that happen to spontaneously get organized in a fitting way survive while those that grew otherwise perish.
 
The following paragraphs from Aristotle could be interpreted as an early understanding of evolution, natural selection, and the survival of the fittest. Charles Darwin is generally credited with that idea, published in his On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1859). Indeed, in the first paragraph of the Preface to his Origin of Species, Darwin himself credits Aristotle for the basic idea, quoting this section of Aristotle’s work!
 
“A difficulty presents itself: why should not nature work, not for the sake of something, nor because it is better so … but of necessity? … Why then should it not be the same with the parts in nature, e.g. that our teeth should come up of necessity-the front teeth sharp, fitted for tearing, the molars broad and useful for grinding down the food-since they did not arise for this end, but it was merely a coincident result; and so with all other parts in which we suppose that there is purpose? Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish,…
 
“It is absurd to suppose that purpose is not present because we do not observe the agent deliberating. Art does not deliberate. If the ship-building art were in the wood, it would produce the same results by nature. If, therefore, purpose is present in art, it is present also in nature. The best illustration is a doctor doctoring himself: nature is like that.

“It is plain then that nature is a cause, a cause that operates for a purpose. [Aristotle, Physics, Book II, Part 8]

 

Chance

Chance covers unusual spontaneous events that are due, in part, to intentional activities or persons capable of moral action.
 
For example, say you are seeking subscriptions for a feast (the Material cause) and you go to a place for some other reason, totally unrelated to seeking subscriptions. There, by chance, you run into a particular person who you had planned to invite. Now, this is not a place you normally go to nor did you know that person would be there. However, at the chance meeting, you do invite him and he buys a subscription (the Final cause).
 
For a cause to be chance, according to Aristotle, the actors must have intended to go the place and/or do what they did for some reason other than the Final cause that resulted from their doing so. In other words, if something comes to be due to actions taken for the sake of something or somethings else, then the first thing may be said to have come about by chance.
 
“Example: A man is engaged in collecting subscriptions for a feast. He would have gone to such and such a place for the purpose of getting the money, if he had known. He actually went there for another purpose and it was only incidentally that he got his money by going there; and this was not due to the fact that he went there as a rule or necessarily, nor is the end effected (getting the money) a cause present in himself-it belongs to the class of things that are intentional and the result of intelligent deliberation. It is when these conditions are satisfied that the man is said to have gone ‘by chance’. If he had gone of deliberate purpose and for the sake of this-if he always or normally went there when he was collecting payments-he would not be said to have gone ‘by chance’.

“It is clear then that chance is an incidental cause in the sphere of those actions for the sake of something which involve purpose. Intelligent reflection, then, and chance are in the same sphere, for purpose implies intelligent reflection.

 
“It is necessary, no doubt, that the causes of what comes to pass by chance be indefinite; and that is why chance is supposed to belong to the class of the indefinite and to be inscrutable to man, and why it might be thought that, in a way, nothing occurs by chance. For all these statements are correct, because they are well grounded. Things do, in a way, occur by chance, for they occur incidentally and chance is an incidental cause. But strictly it is not the cause-without qualification-of anything; for instance, a housebuilder is the cause of a house; incidentally, a fluteplayer may be so.” [Aristotle, Physics, Book II, Part 5]
 
“Hence what is not capable of moral action cannot do anything by chance. Thus an inanimate thing or a lower animal or a child cannot do anything by chance, because it is incapable of deliberate intention; [Aristotle, Physics, Book II, Part 6]
 

Examples of The Four Causes

 
Aristotle gives several examples of causes but he does not always clearly denote which of the Four Causes they exemplify.  In the following tables I have filled in the Four Causes associated with several of his examples. In some cases it was difficult for me to do so. I would appreciate comments that might improve these tables.
 

Causes Related to Human Physiology

 
 Material  Formal  Efficient  Final  
 That out of which That into which That by which  That for the sake of which  Notes
 Human body  Physiology  Drugs, exercise  Health, fitness  a
 Constipation  Physiology  Walking  Move bowels  a
 Mother  Father  Father  Child  a
 Human body  Physiology  Hard work  Fitness  b
 Fitness of body  Physiology  Need for money  Hard work  b

 

a: Human health, illness, reproduction. Walking is Efficient cause of being healthy and also of moving constipated bowels. Father is the Efficient Cause of the child Aristotle seems to ignore the mother’s role other than Material Cause.   ”(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 towards the 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.” 

“For instance, taking a walk [the Efficient cause] is for the sake of evacuation of the bowels [the Final Cause] …” 

“…the primary source of the change or coming to rest; e.g. the man who gave advice is a[n] [Efficient]cause, the father is [Efficient] cause of the child, and generally what makes of what is made and what causes change of what is changed.” [Aristotle, Physics, Book II, Part 3]

b: Reciprocal causes, fitness [Material Cause] enables hard work [Final Cause]. At the same time, hard work [Efficient Cause] causes fitness [Final Cause]. “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 [fitness, the Final Cause] as end, the other [hard work, the Efficient Cause] as the origin of change.” [Aristotle, Physics, Book II, Part 3]

Well-Understood Mechanical Causes

 

 Material  Formal  Efficient  Final  
 That out of which That into which That by which  That for the sake of which  Notes
 Bronze  Image  Sculptor  Statue  c
 Shipping hazard  Mechanics  Ship pilot  Safe passage of ship  d
 Shipping hazard  Mechanics  Absence of ship pilot  Wreck of ship  d

c: Bronze is the Material Cause and the sculptor the Efficient Cause of a statue. “In one sense, then, (1) that out of which a thing comes to be and which persists, is called [Material] ’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.” 

“… both the art of the sculptor [Efficient Cause] and the bronze [Material Cause] 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 [Efficient] cause whence the motion comes. [Aristotle, Physics, Book II, Part 3]
 
d: Same thing as Efficient cause of contrary results. “Further the same thing is the cause of contrary results. For that which by 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 [Final Cause] to the absence of the pilot whose presence was the [Efficient] cause of its safety. [Aristotle, Physics, Book II, Part 3]
 

Causes of Immaterial Things

 

 Material
 Formal
 Efficient
 Final
 
 That out of which
That into which
That by which
 That for the sake of which
 Notes
 Vibration of air
 Relation 2:1 and Number
 Musicial instrument
 Octave
 d
 Letters
 Syllables
 Orator
 Speech
 e
 Premisses
 Formal logic
 Logician
 Conclusion
 f
d: Many modes of causation. Within the same kind one may be prior to another.  “Now the modes of causation are many, though when brought under heads they too can be reduced in number. For ’cause’ is used in many senses and even within the same kind one may be prior to another (e.g. the doctor and the expert are [Efficient] causes of health, the relation 2:1 and number [Formal Causes] of the octave), and always what is inclusive to what is particular. [Aristotle, Physics, Book II, Part 3]
 

e:  Letters are the Material Causes of syllables [Formal Causes]. Premisses are the Material Causes of the Conclusion [Final Cause]. All the causes now mentioned fall into four familiar divisions. The letters are the [Material] 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 [Material] 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 [Efficient Cause] sources whence the change or stationariness originates, while the others are [Final] 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.)  [Aristotle, Physics, Book II, Part 3]

f: Same thing as Efficient cause of contrary results. “Further the same thing is the cause of contrary results. For that which by 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 [Final Cause] to the absence of the pilot whose presence was the [Efficient] cause of its safety. [Aristotle, Physics, Book II, Part 3]
 

Causes Related to Spontaneity and Chance

 

 Material  Formal  Efficient  Final  
 That out of which That into which That by which  That for the sake of which  Notes
 Seeking subscriptions  Incidental opportunity  Chance meeting  Getting subscription  i
 Stone  Incidental happening  Spontaneous fall of a stone  Stone strikes man  j
 Natural things  Natural survival of the fittest  Spontaneous organization in a fitting way  Natural things  k
 

i: Examples of chance causes. Example: A man is engaged in collecting subscriptions for a feast [Material Cause]. He would have gone to such and such a place for the purpose of getting the money [Final Cause], if he had known. He actually went there for another purpose and it was only incidentally that he got his money by going there; and this was not due to the fact that he went there as a rule or necessarily, nor is the end effected (getting the money) a cause present in himself-it belongs to the class of things that are intentional and the result of intelligent deliberation. It is when these conditions are satisfied that the man is said to have gone ‘by chance’. If he had gone of deliberate purpose and for the sake of this-if he always or normally went there when he was collecting payments-he would not be said to have gone ‘by chance’. [Aristotle, Physics, Book II, Part 5]

“Protarchus, for example, said that the stones of which altars are made are fortunate because they are held in honour, while their fellows are trodden under foot. Even these things, however, can in a way be affected by chance, when one who is dealing with them does something to them by chance, but not otherwise.” [Aristotle, Physics, Book II, Part 6]

j: Example of spontaneous but not chance cause.  ”… the spontaneous is even according to its derivation the case in which the thing itself happens in vain. The stone that struck the man did not fall for the purpose of striking him; therefore it fell spontaneously, because it might have fallen by the [purposeful, Efficient Cause]action of an agent and for the purpose of striking [Final Cause]. The difference between spontaneity and what results by chance is greatest in things that come to be by nature; for when anything comes to be contrary to nature, we do not say that it came to be by chance, but by spontaneity. Yet strictly this too is different from the spontaneous proper; for the [Efficient] cause of the latter is external, that of the former internal. [Aristotle, Physics, Book II, Part 6]

k: Nature is the [Material, Formal, and Final] cause of itself. “It is absurd to suppose that purpose is not present because we do not observe the agent deliberating. Art does not deliberate. If the ship-building art were in the wood, it would produce the same results by nature. If, therefore, purpose is present in art, it is present also in nature. The best illustration is a doctor doctoring himself: nature is like that.

“It is plain then that nature is a [Material, Formal, and Final] cause, a cause that operates for a purpose. [Aristotle, Physics, Book II, Part 8]

 

Selected Quotations in Context 

 

Physics, Book II

Part 1. Existence by nature or human-causes.
Of things that exist, some exist by nature, some from other causes.

Part 3. The Four Causes (or explanitory factors) are introduced. 
In one sense, then, (1) that out of which a thing comes to be and which persists, is called [Material] ’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. In another sense (2) the form or the archetype, i.e. the statement of the essence, and its genera, are called [Formal] ’causes’ (e.g. of the octave the relation of 2:1, and generally number), and the parts in the definition. Again (3) the primary source of the change or coming to rest; e.g. the man who gave advice is a[n] [Efficient] cause, the father is cause of the child, and generally what makes of what is made and what causes change of what is changed. Again (4) in the sense of end or ‘that for the sake of which’ a thing is done, e.g. health is the [Final] 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 towards the 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.

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 [Efficient Cause] and the bronze [Material Cause] 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 [Efficient] cause whence the motion comes. 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 [fitness, the Final Cause] as end, the other [hard work, the Efficient Cause] as the origin of change. Further the same thing is the cause of contrary results. For that which by 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 [Final Cause] to the absence of the pilot whose presence was the [Efficient] cause of its safety.

All the causes now mentioned fall into four familiar divisions. The letters are the [Material] 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 [Material] 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 [Efficient Cause] sources whence the change or stationariness originates, while the others are [Final] 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.

 
Now the modes of causation are many, though when brought under heads they too can be reduced in number. For ’cause’ is used in many senses and even within the same kind one may be prior to another (e.g. the doctor and the expert are [Efficient] causes of health, the relation 2:1 and number [Formal Causes] of the octave), and always what is inclusive to what is particular. Another mode of causation is the incidental and its genera, e.g. in one way ‘Polyclitus’, in another ‘sculptor’ is the [Efficient] cause of a statue, because ‘being Polyclitus’ and ‘sculptor’ are incidentally conjoined. Also the classes in which the incidental attribute is included; thus ‘a man’ could be said to be the [Efficient] cause of a statue or, generally, ‘a living creature’. An incidental attribute too may be more or less remote, e.g. suppose that ‘a pale man’ or ‘a musical man’ were said to be the [Efficient] cause of the statue.
 
Part 4. Spontaneity and chance must be accounted for.

Thus we must inquire what chance and spontaneity are, whether they are the same or different, and how they fit into our division of causes.

Part 5. Spontaneity and chance only apply to things that do not come to be by necessity nor always int he same way.
First then we observe that some things always come to pass in the same way, and others for the most part. It is clearly of neither of these that chance is said to be the cause, nor can the ‘effect of chance’ be identified with any of the things that come to pass by necessity and always, or for the most part. But as there is a third class of events besides these two-events which all say are ‘by chance’-it is plain that there is such a thing as chance and spontaneity; for we know that things of this kind are due to chance and that things due to chance are of this kind.

Chance is a subset of spontaneity that applies only when events are for the sake of something, some Final Cause.
But, secondly, some events are for the sake of something [some Final Cause], others not. Again, some of the former class are in accordance with deliberate intention, others not, but both are in the class of things which are for the sake of something. Hence it is clear that even among the things which are outside the necessary and the normal, there are some in connexion withwhich the phrase ‘for the sake of something’ is applicable. (Events that are for the sake of something include whatever may be done as a result of thought or of nature.) Things of this kind, then, when they come to pass incidental are said to be ‘by chance’. For just as a thing is something either in virtue of itself or incidentally, so may it be a cause. For instance, the housebuilding faculty is in virtue of itself the [Efficient] cause of a house, whereas the pale or the musical is the incidental cause. That which is per se [the Efficient] cause of the effect is determinate, but the incidental cause is indeterminable, for the possible attributes of an individual are innumerable. To resume then; when a thing of this kind comes to pass among events which are for the sake of something [some Final Cause], it is said to be spontaneous or by chance. (The distinction between the two must be made later-for the present it is sufficient if it is plain that both are in the sphere of things done for the sake of something.)

Example: A man is engaged in collecting subscriptions for a feast [the Material Cause]. He would have gone to such and such a place for the purpose of getting the money, if he had known. He actually went there for another purpose and it was only incidentally that he got his money by going there; and this was not due to the fact that he went there as a rule or necessarily, nor is the end effected (getting the money) a [Final] cause present in himself-it belongs to the class of things that are intentional and the result of intelligent deliberation. It is when these conditions are satisfied that the man is said to have gone ‘by chance’. If he had gone of deliberate purpose and for the sake of this-if he always or normally went there when he was collecting payments-he would not be said to have gone ‘by chance’.

It is clear then that chance is an incidental cause in the sphere of those actions for the sake of something [some Final Cause] which involve purpose. Intelligent reflection, then, and chance are in the same sphere, for purpose implies intelligent reflection.

Why some think that nothing occurs by chance! Aristotle seems to agree with that idea, which corresponds to Spinoza and Einstein’s deterministic views.
It is necessary, no doubt, that the causes of what comes to pass by chance be indefinite; and that is why chance is supposed to belong to the class of the indefinite and to be inscrutable to man, and why it might be thought that, in a way, nothing occurs by chance. For all these statements are correct, because they are well grounded. Things do, in a way, occur by chance, for they occur incidentally and chance is an incidental cause. But strictly it is not the cause-without qualification-of anything; for instance, a housebuilder is the cause of a house; incidentally, a fluteplayer may be so.

And the causes of the man’s coming and getting the money (when he did not come for the sake of that) are innumerable. He may have wished to see somebody or been following somebody or avoiding somebody, or may have gone to see a spectacle. Thus to say that chance is a thing contrary to rule is correct. For ‘rule’ applies to what is always true or true for the most part, whereas chance belongs to a third type of event. Hence, to conclude, since causes of this kind are indefinite, chance too is indefinite. (Yet in some cases one might raise the question whether any incidental fact might be the cause of the chance occurrence, e.g. of health the fresh air or the sun’s heat may be the cause, but having had one’s hair cut cannot; for some incidental causes are more relevant to the effect than others.)

Chance or fortune is called ‘good’ when the result is good, ‘evil’ when it is evil. The terms ‘good fortune’ and ‘ill fortune’ are used when either result is of considerable magnitude. Thus one who comes within an ace of some great evil or great good is said to be fortunate or unfortunate. The mind affirms the essence of the attribute, ignoring the hair’s breadth of difference. Further, it is with reason that good fortune is regarded as unstable; for chance is unstable, as none of the things which result from it can be invariable or normal.

Both are then, as I have said, incidental causes-both chance and spontaneity-in the sphere of things which are capable of coming to pass not necessarily, nor normally, and with reference to such of these as might come to pass for the sake of something.

Part 6. Spontaneity is the wider term, chance is a subset applicable ony to agents who are capable of moral action.. 
They differ in that ‘spontaneity’ is the wider term. Every result of chance is from what is spontaneous, but not everything that is from what is spontaneous is from chance.

Chance and what results from chance are appropriate to agents that are capable of good fortune and of moral action generally. Therefore necessarily chance is in the sphere of moral actions. This is indicated by the fact that good fortune is thought to be the same, or nearly the same, as happiness, and happiness to be a kind of moral action, since it is well-doing. Hence what is not capable of moral action cannot do anything by chance. Thus an inanimate thing or a lower animal or a child cannot do anything by chance, because it is incapable of deliberate intention; nor can ‘good fortune’ or ‘ill fortune’ be ascribed to them, except metaphorically, as Protarchus, for example, said that the stones of which altars are made are fortunate because they are held in honour, while their fellows are trodden under foot. Even these things, however, can in a way be affected by chance, when one who is dealing with them does something to them by chance, but not otherwise.

Spontaneity (but not chance) applies to lower animals and inanimate objects.
The spontaneous on the other hand is found both in the lower animals and in many inanimate objects. We say, for example, that the horse came ‘spontaneously’, because, though his coming saved him, he did not come for the sake of safety. Again, the tripod fell ‘of itself’, because, though when it fell it stood on its feet so as to serve for a seat, it did not fall for the sake of that.

Hence it is clear that events which (1) belong to the general class of things that may come to pass for the sake of something [some Final Cause], (2) do not come to pass for the sake of what actually results, and (3) have an external cause, may be described by the phrase ‘from spontaneity’. These ‘spontaneous’ events are said to be ‘from chance’ if they have the further characteristics of being the objects of deliberate intention and due to agents capable of that mode of action. This is indicated by the phrase ‘in vain’, which is used when A which is for the sake of B, does not result in B. For instance, taking a walk is for the sake of evacuation of the bowels; if this does not follow after walking, we say that we have walked ‘in vain’ and that the walking was ‘vain’. This implies that what is naturally the means to an end is ‘in vain’, when it does not effect the end towards which it was the natural means-for it would be absurd for a man to say that he had bathed in vain because the sun was not eclipsed, since the one was not done with a view to the other. Thus the spontaneous is even according to its derivation the case in which the thing itself happens in vain. The stone that struck the man did not fall for the purpose of striking him; therefore it fell spontaneously, because it might have fallen by the action of an agent and for the purpose [FInal Cause] of striking. The difference between spontaneity and what results by chance is greatest in things that come to be by nature; for when anything comes to be contrary to nature, we do not say that it came to be by chance, but by spontaneity. Yet strictly this too is different from the spontaneous proper; for the cause of the latter [spontaneity] is external, that of the former [chance] internal.

We have now explained what chance is and what spontaneity is, and in what they differ from each other. Both belong to the mode of causation ‘source of change’, for either some natural or some intelligent agent is always the cause; but in this sort of causation the number of possible causes is infinite.

Spontaneity and chance are [Efficient] causes of effects which though they might result from intelligence or nature, have in fact been caused by something incidentally. Now since nothing which is incidental is prior to what is per se, it is clear that no incidental cause can be prior to a cause per se. Spontaneity and chance, therefore, are posterior to intelligence and nature. Hence, however true it may be that the heavens are due to spontaneity, it will still be true that intelligence and nature will be prior causes of this All and of many things in it besides. 

 
Part 8. The first paragraph of Part 8 seems to pressage evolution and natural selection and survival of those most fit to the environment, over 2000 years before Charles Darwin, in 1859, published his Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Darwin himself quotes and paraphrases parts of this paragraph.
A difficulty presents itself: why should not nature work, not for the sake of something, nor because it is better so, but just as the sky rains, not in order to make the corn grow, but of necessity? What is drawn up must cool, and what has been cooled must become water and descend, the result of this being that the corn grows. Similarly if a man’s crop is spoiled on the threshing-floor, the rain did not fall for the sake of this-in order that the crop might be spoiled-but that result just followed. Why then should it not be the same with the parts in nature, e.g. that our teeth should come up of necessity-the front teeth sharp, fitted for tearing, the molars broad and useful for grinding down the food-since they did not arise for this end, but it was merely a coincident result; and so with all other parts in which we suppose that there is purpose? Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish, as Empedocles says his ‘man-faced ox-progeny’ did. 
 
Further, where a series has a completion, all the preceding steps are for the sake of that. Now surely as in intelligent action, so in nature; and as in nature, so it is in each action, if nothing interferes. Now intelligent action is for the sake of an end; therefore the nature of things also is so. Thus if a house, e.g. had been a thing made by nature, it would have been made in the same way as it is now by art; and if things made by nature were made also by art, they would come to be in the same way as by nature. Each step then in the series is for the sake of the next; and generally art partly completes what nature cannot bring to a finish, and partly imitates her. If, therefore, artificial products are for the sake of an end, so clearly also are natural products. The relation of the later to the earlier terms of the series is the same in both. This is most obvious in the animals other than man: they make things neither by art nor after inquiry or deliberation. Wherefore people discuss whether it is by intelligence or by some other faculty that these creatures work,spiders, ants, and the like. By gradual advance in this direction we come to see clearly that in plants too that is produced which is conducive to the end-leaves, e.g. grow to provide shade for the fruit. If then it is both by nature and for an end that the swallow makes its nest and the spider its web, and plants grow leaves for the sake of the fruit and send their roots down (not up) for the sake of nourishment, it is plain that this kind of cause is operative in things which come to be and are by nature. And since ‘nature’ means two things, the matter and the form, of which the latter is the end, and since all the rest is for the sake of the end, the form must be the cause in the sense of ‘that for the sake of which’. 
 
It is absurd to suppose that purpose is not present because we do not observe the agent deliberating. Art does not deliberate. If the ship-building art were in the wood, it would produce the same results by nature. If, therefore, purpose is present in art, it is present also in nature. The best illustration is a doctor doctoring himself: nature is like that.

It is plain then that nature is a cause, a cause that operates for a purpose [a Final cause that is nature itself!].