TEN DIALOGUES OF NATURAL PHILOSOPHY
Translation © George MacDonald Ross, 1998–1999
Chapter 1: The origin of natural philosophy
A. [71] There is a kind of thing which I do not understand well, which is called ‘philosophy’. I have heard it very highly recommended, and it is much talked about by people who do not have much else to do. But I have also heard it despised and derided by others; so I cannot tell whether it is good or bad, nor what to make of it, although I see many other people doing well by it.
B. I have no doubt that anything which so many people praise so highly must be very admirable, and anything which many people deride and hold in contempt must be foolish and ridiculous. But ultimately the respect and contempt are directed, not at philosophy itself, but at its practitioners. Philosophy is the knowledge of natural causes; and there is no knowledge except of the truth. To know the true causes of things has never been held in contempt, but only in admiration. Scorn can never get a hold on truth. The difference is entirely between the writers and teachers. Some of them have worked at it or been concerned for it only as a job which provides a salary or is a step to a better job. Others have studied it because it is fashionable, and to make it possible for them to associate with clever people; and their study has not consisted in thinking it through, but in accepting the authority of the authors they have [72] heard recommended. Only a few have studied it out of curiosity, and for the pleasure which people usually get from acquiring knowledge, and mastering difficult and abstruse subjects. Among these I include Aristotle and a few other ancient philosophers, and a few moderns. These are the people who genuinely deserve the praises which are given to philosophy.
A. If I want to study natural philosophy, for example, does this mean I have to read Aristotle, or some of the authors who are currently in fashion?
B. There is no necessity for it. However, if you come up against a problem in your own thinking, I do not think it a waste of time to find out what other people say about it, provided that you rely only on your reason. The ancient philosophers gave very reasonable explanations, which anyone can agree with, of a few natural phenomena, especially in astronomy. For example, they explained eclipses of the sun and moon by long observation, and by calculating their apparent motions. But what is that in comparison with the innumerable everyday phenomena of nature? Which of them or their successors have given you satisfactory explanations of gravity, heat, cold, light, sensation, colour, noise, rain, snow, frost, winds, the tides of the sea, and a thousand other things? A few people’s lives are too short to cover all these. You and other people with inquiring minds find them amazing (despite their being daily occurrences), and would love to know their causes; but you will not find them in the books written by natural philosophers. If you ask any of today’s philosophers what the causes of any of them are, you will be fobbed off with mere words. Fully analysed, these words signify nothing [73] whatever more than ‘I cannot tell,’ or ‘because it is’ — for example, ‘intrinsic quality’, ‘occult quality’, ‘sympathy’, ‘antipathy’, ‘antiperistasis’, and the such like. Words like these have currency among people who have little concern for such wisdom, even though they are wise enough in their own ways. But they will have no currency with you, who are asking not simply what the cause is, but how it comes about that such effects are produced.
A. It is a fraud. But why was fraud necessary? When did they begin to play the charlatan in this way?
B. It wasn’t necessary. But don’t you know that, from their very birth, people instinctively fight each other for everything they want, and would have the whole world fear and obey them, if they could? If by luck or hard work someone chances upon one of nature’s secrets, and thereby gains the reputation of being an exceptionally knowledgeable person, why should they not use it to their own advantage? There is hardly one in a thousand who would not live at other people’s expense as far as they dare. What poor geometrician is there who does not take pride in being thought a magician? What quack wouldn’t make a living out of a false opinion that they were a great doctor? And when many of them are simultaneously engaged in upholding a false doctrine, they will close ranks so as to maintain their authority to suppress the truth.
A. Please tell me, if you can, how and where the study of philosophy first began.
B. If we can believe the ancient historians, the first to study any of the natural sciences were the astronomers of Ethiopia. My authority for this is Diodorus Siculus, [n.1] who has a high reputation for accuracy. [74] He begins his history from the earliest possible times, and tells us that the first astronomers were in Ethiopia. Because of their predictions of eclipses, and other conjunctions and aspects of the planets, not only did their king grant them towns and fields amounting to a third of the whole land, but they were also so revered by the people that they were thought to be in communication with the gods, which were the stars. This made their kings stand in awe of them, so that they dared to eat and drink only what and when the astronomers prescribed — indeed, they didn’t even dare to continue living, if the astronomers said that the gods commanded them to die. And so they remained in subjection to their false prophets until one of their kings, called Ergamenes (about the time of the Ptolemies [n.2]) had them put to the sword.
But long before the time of Ergamenes, the astrologer caste (the profession was kept within the family) had become so numerous, that many of them emigrated to Egypt (I don’t know if they were invited or not). [n.3] There too they were allocated cities and lands, and were in demand, not only for their astronomy and astrology, but also for their geometry. At the time, Egypt was, as it were, a university for the whole world, and Greeks with enquiring minds went there in order to bring philosophy to Greece — for example, Pythagoras, Plato, Thales, and others. [n.4]
But long before that time, many of the Ethiopian astrologers had gone to Assyria, [n.5] where they were also allocated towns and lands. This group were called ‘Chaldees’ by the Hebrews.
A. Why so?
B. I don’t know. But according to Martinius’s Lexicon, they are called ‘Chasdim’ and ‘Chesdim’, in his opinion from someone called Chesed, the son of Nachor. But I [75] cannot find any such person as Chesed among the descendants of Noah in the Bible. Nor do I find that there was any specific country called Chaldaea, [n.6] although any town where any of them lived was called a town ‘of the Chaldees’. In addition, Martinius says that the same word ‘chasdim’ also means ‘demons’.
A. Arguing in this way, I would conjecture that they were called Chusdim because they were a caste of Ethiopians. The land of Chus is Ethiopia, and the name degenerated first into Chuldim, and then into Chaldim. So they had the same kind of social identity as gypsies, [n.7] except that the Chaldeans were admired and feared for their trickery, whereas gypsies were considered to be rogues.
B. Yes, but with the exception of Claudius Ptolomaeus, the author of that great work of astronomy, the Almagest.
A. I accept that he excelled both in astronomy and in geometry, and that his Almagest is a commendable work. But his Judicial Astrology, [n.8] which is appended to it, makes him a gypsy again. But as for the Greeks who you say travelled to Egypt, what philosophy did they take home with them?
B. Mathematics and astronomy. As far as I have read, the Greeks were the first people to study terrestrial physics, which is usually called ‘natural philosophy’; and it was taken over from them by the Romans. Yet both Greeks and Romans were more interested in moral than in natural philosophy. Their extant writings on moral philosophy were loose and unsystematic, based on no principles other than their own passions and prejudices, without any reference to the laws of the state, which are the basis and criterion [76] of all true morality. Consequently, their books tend to teach people to criticise the laws rather than to obey them; which has been a great obstacle to the peace of the western world ever since. Only a few of them seriously applied themselves to natural philosophy — for example, Plato and Aristotle, whose works are extant, and Epicurus, whose teachings have been preserved through Lucretius. The writings of Philolaus and many other researchers with enquiring minds are now lost, because they were burnt or neglected. However, the theory of Philolaus that the Earth revolves round the sun has been revived by Copernicus, and explained and confirmed by the late Galileo.
A. I think the natural philosophy of Plato, Aristotle, and the rest should have been developed and made to flourish by their disciples.
B. Who do you mean by the successors of Plato, Epicurus, Aristotle, and the other founders of philosophical schools? Perhaps some of them may have been learned and worthy people. But not long after, and down to the time of our Saviour and his apostles, they were mostly a crowd of impoverished, ignorant, shameless, and dishonest fellows, who got their living by regurgitating the teachings of the founders of their schools. At the time, philosophy was so fashionable and respected by important people, that anyone who could afford it had a philosopher of one sect or another to be a tutor to their children. It was these tutors who pretended to be Christians, and with their powers of argument and eloquence, got themselves into the Christian community, and imported so many heresies into the primitive Church, each one retaining a flavour of their previous doctrines.
A. [77] But these heresies were all condemned at the first Council, which was held at Nicaea.
B. Yes. But the Arian heresy as well as the Roman one flourished for a long time, and was upheld by various emperors, and never completely stamped out as long as there were Vandals in Christendom. Besides, new heresies kept on appearing, consisting in philosophical positions which contradicted the teaching of the Councils on questions such as the divinity of our Saviour, how many persons he was, and how many natures he had. It continued like this until the time of Charlemagne , when he and Pope Leo III divided the power of the Empire into the temporal and the spiritual.
A. A very unequal division.
B. Why? Which of them do you think had the greater share?
A. No doubt the Emperor, since he alone had the sword.
B. But swords are in the hands of people. Would you prefer to have control over the swords, or over the people who wield them?
A. I understand what you mean. The person who controls people’s hands has the use both of their swords and of their strength.
B. Now that the Empire was divided into the spiritual and the temporal, the freedom of philosophy was very dangerous to the spiritual power. For that reason, the Pope had to establish schools, not only for divinity, but also for other sciences, especially natural philosophy. He used the power of the Emperor to achieve this; and there arose a new science called ‘school divinity’, consisting in a mixture of Aristotle’s metaphysics and the Bible. This has remained the principal learning in [78] Western Europe from the time of Charlemagne till very recently.
A. I can’t find anything in the writings of the scholastic philosophers which says how the causes they assign to things naturally and necessarily produce their effects.
B. You should not be surprised at this. When you see a change in anything, your concern is not so much with what its cause might be said to be, but with how the change comes into being. This coming into being is the entire natural process from the efficient cause to the effect which is produced. This is always a difficult question, and mostly impossible for a human to give an answer to, since the alterations in the things we perceive by our five senses are brought about by motions of bodies which are mostly invisible, either because they are too far away, or because they are too small, or because they are transparent.
A. But why did they have to assign any causes at all, given that they could not show how their effects followed from them?
B. As I said, the schools were founded by the Pope and Emperor, but governed by the Pope alone, in order to answer and refute the heresies of the philosophers. Would you expect them to betray their mission and authority, that is to say their livelihood, by admitting their ignorance? They preferred to uphold their mission and authority by replacing causes with strange and unintelligible words, which would be adequate enough for the purpose, not only of satisfying their paymasters, but also of making it difficult for the philosophers themselves to find fault with them.
A. Since you say that alteration is brought about by the motion of bodies, can you please first tell me what I am to understand by the word ‘body’?
B. [79] This is a difficult question, even though most people think it can be answered easily, by saying that it is whatever they can see, feel, or become aware of through their senses. But if you want to know what body really is, we must first ask what there is which is not body. I am sure you must have seen how mirrors can have the effect of multiplying or magnifying the objects of sight. For example, a mirror of a certain shape will make a token or a shilling seem twenty, even though you know perfectly well that there is only one. And if you try to identify it by putting a mark on it, you will find the mark on all of them. The counter is certainly one the things we call ‘bodies’. So are not the others also bodies?
A. No, obviously not, since looking in a mirror cannot make them really more than they are.
B. What, then, are they other than phantasms — so many phantasms of one and the same thing in different places?
A. It is obvious that they are so many idols, mere nothings.
B. When you look at a star or a candle with both your eyes, but make one of them slightly squint with your finger, do you not see two stars, or two candles? And even if you call it a visual illusion, you cannot deny that there are two images of the object.
A. This is true, and something which everybody has observed. And I say the same of our faces seen in mirrors, and of all dreams, and of all apparitions of dead people’s ghosts. Since it is so obvious, I am surprised I never thought of it before. But it is a very pleasant surprise, and since it is well understood by everybody, it should utterly destroy both idolatry and superstition, and defeat the many frauds who cheat and trouble the world with their tricks.
B. [80] But you must not conclude from this, that everyone who interprets their dreams, and is sometimes guided by them, is therefore an idolater, or superstitious, or a fraud, since God does often tell people what they ought to do through their dreams. But in this case, people must be careful not to base the way they live their lives on their dreams beyond what is allowed by the laws of their country. You know what God says in Deuteronomy 13: ‘If a prophet or dreamer of dreams gives you a sign or a miracle, and the sign comes to pass, yet if he tells you to serve other gods, then let him be put to death.’ Here, ‘serving other gods’ means revolting against their King, or disobeying his laws, since they have chosen God as their king. Otherwise I see no idolatry or superstition in following a dream, as did many of the patriarchs in the Old Testament, and saints in the New Testament.
A. Yes, their own dreams. But when someone else dreams, or say they have dreamed, and tell me to follow their dream, they must excuse me if I ask them by what authority, especially if they expect me to pay them for it.
B. But if required by the laws you live under, you ought to follow it.
Now, when one sound gives rise to various echoes, what are these echoes? And when you grasp a little ball with your fingers crossed, and think there are two; and when the same herb or flower smells nice to one person and nasty to another, or nice and nasty to yourself at different times; and the same with tastes: then what are these echoes, feelings, smells, and tastes?
A. It is obvious that they are all only phantasms. But certainly when the sun seems to my eye no bigger [8] than a plate, there is something else somewhere behind it, which I suppose to be the real sun, which creates these phantasms, by having some sort of influence on my eyes, and other sense organs, so as to cause a variety of phantasms.
B. What you say is correct; and this is what I mean by ‘body’, which I briefly define as anything which exists independently of being perceived.
A. I think what Aristotle means by ‘body’ is a ‘substance’ or ‘subject’, which colour, sound, and other phantasms ‘inhere in’, to use his expression. The word ‘essence’ has nothing to do with substance. Seneca says he cannot understand the word; and no wonder, since the word ‘essence’ does not belong to ordinary language, but is a word coined by philosophers out of the copula which joins two names into a proposition. It is as if someone who had two hounds could make a third, if they needed it, out of the brace [n.9] holding them together.
B. Just so. Having said mentally, ‘A tree is a plant,’ for example, they had an adequate conception of the meanings of ‘tree’ and ‘plant’, but did not know what to make of the word ‘is’, which joins the names together. Not daring to call it a body, they called it by a new name essentia (derived from the word est), and substantia. In doing so they were misled by the peculiar idiom of their own language. In many other languages, for example Hebrew, there is no such copulative verb. The Hebrews thought that the names of things were sufficiently connected by being placed in their natural order; so they were never troubled by ‘essences’, or any other fallacies deriving from the copulative verb est.
Chapter 2: The principles and method of natural philosophy
A. [82] This history of ancient philosophy has not put me out of love with philosophy, but it has put me out of hope of getting it out of any of their writings. I would therefore like to try and attain knowledge of it by working it out for myself. But I do not know where to begin, or how to proceed.
B. You say your desire is to know the causes of the effects, or phenomena of nature. You agree that they are phantasms, and consequently that they are in yourself. So only the causes you are looking for are external to yourself; and now you want to know how these external bodies affect you so as to produce those phenomena. Therefore you ought to begin your enquiry by asking the question: ‘What is it that you call a ‘cause’?’ I mean an ‘efficient’ cause. For philosophers distinguish between four kinds of causes, of which the efficient cause is one. Another they call the ‘formal’ cause, or simply the ‘form’ or ‘essence’ of the thing which is caused; as when they say that ‘four equal angles and four equal sides are the cause of a square figure,’ or that ‘heaviness is the cause which makes heavy bodies descend.’ But this is not the kind of cause you are looking for, since it amounts to no more than ‘It descends because it descends.’ The third is the ‘material’ cause, as when they say that the walls and roof, etc. of a house are the cause of the house. The fourth is the ‘final’ cause, which belongs only to moral philosophy.
A. [83] We shall think about final causes on some other occasion; but not at all about formal or material causes. I am looking only for efficient causes, and how they act, from the beginning to the production of the effect.
B. I say, then, that in the first place you must enquire thoroughly into the nature of motion, since the differences between one phantasm and another, or (which is the same thing) between one phenomenon of nature and another, all have one universal efficient cause, namely the differences between one motion and another. If all the things in the world were absolutely at rest, there could be no difference between one phantasm and another, and living creatures would be without any sensation of objects; which is hardly less than to be dead.
A. Suppose a new-born baby is exposed to the blue sky with its eyes open. Do you not think that it would have some sensation of the light, but that everything would seem dark to the baby?
B. Yes. If it had no memory of anything it had seen before, or perceived by any of the other senses (which is what we are assuming), I think it would be in the dark. For darkness is darkness, whether it is black or blue, to someone who cannot make the distinction.
A. Whatever the answer to this, it is obvious enough that whatever has an effect on the sense organs is in motion, since action is motion.
B. Having given careful consideration to the nature of motion, you must make it the starting point and foundation for your enquiry.
A. How?
B. Explain as fully and as briefly as you can what you always mean by ‘motion’. This will save yourself as well as others from being misled by ambiguity.
A. Then I say that motion is nothing other than change of [84] place, since the whole effect of a body on our sense organs is nothing but a phantasm. Therefore the only phantasm we can have as the result of seeing a body move is change of place.
B. That is right. But you must next tell me what you mean by ‘place’, since not everyone agrees about that.
A. Well then, when we phantasise a body, we cannot help phantasising it somewhere. Therefore I think that place is the phantasm of here or there.
B. That is not enough. ‘Here’ and ‘there’ are understood by no-one but yourself, unless you point to something. But pointing is not a part of a definition. Besides, although pointing might help someone find a place, it will never actually take them to it.
A. But since sensation is a phantasm, when we phantasise a body, we also phantasise its shape, and the space it occupies. So now I can define ‘place’ as the exact space which contains the body. For space is alo part of the image we have of the object which is seen.
B. And how do you define time?
A. I think time has the same relation to the motion of a body, as place has to the body itself. Consequently, I take time to be our phantasm or image of its motion. But is all this precise detail really necessary?
B. Yes. The lack of it is the main, if not the only cause of all the disagreements among philosophers. You can easily perceive this from the way they misuse and confuse the names of things which have different natures, as you will see when it is appropriate to quote some of the tenets of various philosophers.
A. I shall avoid ambiguity as much as I can. [85] As for the nature of motion, I assume that I understand it from its definition. What is to be done next?
B. From these definitions, and from any other truth you know by the light of nature, you must draw general consequences which will serve as axioms, or principles for your reasoning.
A. That is hard to do.
B. I shall draw them myself, or at any rate as many as we need for our present dialogue on natural causes. Your role will be no more than to take care that I do not deceive you.
A. I shall take care.
B. My first axiom, then, will be this: Two bodies cannot be in one place at the same time.
A. That is true, since we count bodies as we phantasise them as distinct, and we distinguish them by their places. You can therefore add that one body cannot be in two places at the same time. Philosophers mean the same when they say ‘There is no penetration of bodies.’
B. But they do not understand their own words, since this is not what ‘penetration’ means. My second axiom is that nothing can begin, change, or put an end to its own motion. Suppose it begins exactly now; or suppose it is already in motion, and now changes direction, or stops. I ask the reason why it should happen now, rather than before or after, since it has all that is necessary for such motion, change, or coming to rest, equally at all times.
A. I have no doubt that the argument is valid for inanimate bodies; but perhaps it does not hold for voluntary agents.
B. We shall consider how it holds for voluntary agents when our method brings us to [86] the powers and passions of the mind. The third axiom will be this: Any body at rest which is subsequently moved, is directly moved by some other body which is in motion and touches it. Since nothing can move itself, the body which causes the motion must be external. And because motion is change of place, the body which causes the motion must displace the body it moves, which it cannot do until it touches it.
A. That is obvious; and also that it must not simply touch it, but that it must follow it into its place. And if more parts of the body are moved than are touched by the body moving it, the body causing the motion is not the direct cause of their motion. This is why, in the case of a continuous body, however large it is, if its first surface is pushed back, however slightly, the motion will proceed right through it.
B. Do you think this is impossible? I shall prove it from your own words. You say that the body causing the motion touches the body it moves at the time it moves it. Therefore it pushes it back; but that which is pushed back pushes back what is immediately behind it; and that pushes the next, and so onwards to any distance, as long as the body continues. This is also obvious from experience, since someone walking with a stick can distinguish between stone and glass, even if they are blind; but this would be impossible if the parts of the stick between the ground and the hand offered no resistance. This is also why, in the silence of the night, you can hear footsteps from a greater distance if you put your ear to the ground, than if you are standing upright.
A. This is certainly true of a walking stick or other solid body, because it prevents the motion in a straight line from being diffused. But in a fluid body such as the air, the part which is pushed back must fill an orb, [n.10] and [87] the further it is pushed back, the larger the orb it has to fill. Consequently, the motion will decrease, and eventually come to an end because of the resistance of the air.
B. I do not think it is true that any body in the world is absolutely at rest. However, I do admit that, in a volume completely filled with body, however fluid, if you set any part of it in motion, the motion will become less and less, and eventually cease, because of the resistance of the parts which are moved. But if you assume that the volume is a perfect vacuum, and has nothing in it at all, then anything which is once set in motion will go on for ever; otherwise what you have already accepted is not true, namely that nothing can put an end to its own motion.
A. But what do you mean by ‘resistance’?
B. Resistance is the motion of a body in a direction which is wholly or partly opposite to the direction of that which sets it in motion, and which thereby forces it back, or slows it down. For example, when you run fast, you feel the motion of the air on your face. But when two solid bodies meet, it is much more obvious how they slow each other down, and bounce away from each other. For in a space which is already full, the motion cannot be instantaneously propagated through to the other end of the body which is to be moved.
A. What other definitions do I need?
B. In quantifying anything, you must start from the smallest quantity it is possible to assume. This is also true of motion, and you should begin with the smallest possible motion. It is what I call the first ‘conation’ of the body causing the motion; and this conation, however weak, is also a motion. For if it had no effect at all, it would still have no effect if it were doubled, trebled, or multiplied by any number whatever, since nothing multiplied by anything is still nothing. We shall bring in other [88] axioms and definitions incidentally, as we need them.
A. Is this all the preparation I need to make?
B. No. You also need to consider the various kinds and properties of motion. For example, when a body is set in motion by one or more moving bodies at the same time, you need to consider whether the resultant motion will be in a straight line, a circle, or some other curve — and also what its speed will be. Again, you need to consider whether the body causing the motion acts by pushing, carrying, hitting, reflecting, or refracting. Beyond this, you need to supply yourself with as many observations (which are called phenomena) as you can. Then, when you are looking for the cause of a phenomenon you have observed, assume some specific motion as its cause, and test whether you can derive the cause you are looking for from your assumption by evident reasoning, and without contradicting any other obvious truth or observation. If you can, it is all that can be hoped for from philosophy as to that particular question. For there is no effect in nature which the Author of nature cannot bring about by more ways than one.
A. I am happy enough to know the causes of the phenomena which belong to everyday experience. But please do bring up any which I do not know about, and which you can add from your own personal observations, or from books recording other people’s observations of nature which you know to be reliable. Let us now therefore look into the cause of some particular effect.
B. We shall begin with the one which is the most universal, namely the universe itself. And first we shall consider the question whether there is any place which is absolutely empty, or, to use the language of philosophers, whether there is any vacuum in nature.
A. [89] It is difficult to take as an assumption, and even more difficult to believe, that the infinite and omnipotent Creator of all things should have produced something as vast as the world we see, without leaving a few little spaces with nothing at all in them. Relative to the universe as a whole, they would be insignificant.
B. Why do you say that? Do you think it provides any argument to prove there is a vacuum?
A. Why not? Given the rapid vibration of all natural bodies, why should not some small parts of them be thrown off, and leave empty the places they were thrown out of?
B. Because He who created them is not a phantasm, but the most real substance that exists. Since he is infinite, no place where He is can be empty, and no place where He is not can be full. . . . .
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