The Essential Galileo (34 page)

S
AGR.
   . This way of all knowledge being contained in a book is very similar to that by which a piece of marble contains within itself a very beautiful statue, or a thousand of them for that matter; but the point is to be able to discover them. We can say that it is also similar to Joachim's
¹³
prophecies or to the answers given by heathen oracles, which are understood only after the occurrence of prophesied events.

[136] S
ALV.
    And where do you leave the predictions of astrologers,
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which after the event can be so clearly seen in the horoscope, or should we say in the configuration of the heavens?

S
AGR.
    In the same vein alchemists,
¹⁵
driven by their melancholic humor, find that all the greatest minds in the world have never written about anything except the process of making gold, but that, in order to say this without revealing it to the common people, they
have contrived in various ways to conceal it under various covers. It is very amusing to listen to their comments on ancient poets, as they reveal the very important mysteries lying hidden under those fables:
¹⁶
what is the meaning of the love affairs of the moon, of her coming down to earth for Endymion, and of her anger at Actaeon; when does Jupiter change himself into golden rain, and when into burning flames; and how many great secrets of the art are to be found in Mercury the interpreter, in Pluto's kidnappings, and in those golden boughs.

S
IMP.
    I believe and to some extent know that the world is full of very extravagant brains, whose follies should not redound to the discredit of Aristotle. You seem sometimes to speak of him with too little respect, but the mere antiquity and the great name he has acquired in the minds of so many outstanding men should suffice to make him respectable among all educated men.

S
ALV.
    That is not the way it is, Simplicio. It is some of his excessively cowardly followers who are responsible for making us think less of him, or to be more exact, who would be so responsible should we want to applaud their triflings. Tell me, if you do not mind, are you so simple minded that you do not understand that if Aristotle had been present to listen to the doctor who wanted to make him inventor of the telescope, he would have been more angry with him than with those who were laughing at the doctor and his interpretations? Do you have any doubt that if Aristotle were to see the new discoveries in the heavens, he would change his mind, revise his books, accept the more sensible doctrines, and cast away from himself those who are so weak minded as to be very cowardly induced to want to uphold every one of his sayings? Do they not realize that if Aristotle were as they imagine him, he would be an intractable brain, an obstinate mind, a barbarous soul, a tyrannical will, someone who, regarding everybody else as a silly sheep, would want his decrees to be preferred [137] over the senses, experience, and nature herself? It is his followers who have given authority to Aristotle, and not he who has usurped or taken it. Since it is easier to hide under someone else's shield than to show oneself openly, they are afraid and do not dare to go away by a single step; rather than putting any changes in the heavens of Aristotle, they insolently deny those which they see in the heavens of nature.

S
AGR.
    These people make me think of that sculptor who carved a large piece of marble into an image of Hercules or of a thundering Jupiter (I forget which); with admirable skill he gave it so much liveliness and fierceness that it terrified anyone who looked at it; then he himself began to be afraid even though these qualities were the work of his own hands; and his terror was such that he no longer dared to face him with his chisel and mallet.

S
ALV.
    I have often wondered how it can be that those who rigidly maintain everything Aristotle said do not notice how much damage they do to his reputation, how much discredit they bring him, and how much they diminish his authority instead of increasing it. For I often see them stubbornly wanting to defend propositions that I find palpably and manifestly false, and wanting to persuade me that this is what a true philosopher is supposed to do and what Aristotle himself would do; their behavior greatly undermines my belief that he may have philosophized correctly in regard to other conclusions less well known to me; on the other hand, if I saw them yielding and changing their minds in regard to the obvious truths, I would be inclined to believe that when they persisted they might have sound demonstrations which I did not know or understand.

S
AGR.
    Still, if they felt they were risking too much of Aristotle's reputation or their own by admitting not knowing this or that conclusion discovered by others, would it not be better to find it in his texts by combining them in accordance with the practice mentioned by Simplicio? For, if all knowledge is contained there, one must be able to find it.

S
ALV.
    Sagredo, do not make fun of this advice, which you seem to propose in jest. In fact, not long ago a philosopher of great renown wrote a book on the soul which discussed Aristotle's opinion on whether or not the soul is immortal by presenting many passages that suggested a pernicious answer (these were passages discovered by himself in little known places rather than the ones quoted by Alexander
¹⁷
[138] because in these Aristotle allegedly did not even discuss this subject, let alone establish anything pertaining to it); when he was warned that he would have encountered difficulties in getting the printing license, he wrote back to his friend not to let this stop the application process because, if there were no other obstacles, he would have had no difficulty changing Aristotle's doctrine and supporting the contrary opinion with other assertions and passages also corresponding to Aristotle's mind.

S
AGR.
    Oh, what a scholar! I am at his command; he does not want to be duped by Aristotle, but wants to lead him by the nose and make him speak as he himself commands! See how important it is to know how to seize an opportunity. One should not deal with Hercules when he is in a rage and overtaken by fury, but rather while he is playing with Lydian maids.
¹⁸
Oh, the unbelievable cowardice of slavish minds! To make oneself spontaneously a slave, to accept decrees as inviolable, to be obliged to call oneself persuaded and convinced by arguments so effective and clearly conclusive that its proponents cannot decide even whether they are written for that purpose and are meant to prove that conclusion! But let us mention the greatest folly: that they themselves are still uncertain whether the same author holds the affirmative or negative side. Is not this like regarding a wooden statue as their oracle, resorting to it for answers, fearing it, revering it, and worshipping it?

S
IMP.
    But, if one abandons Aristotle, who will be the guide in philosophy? Name some author.

S
ALV.
    One needs a guide in an unknown and uncivilized country, but in a flat and open region only the blind need a guide; whoever is blind would do well to stay home, whereas anyone who has eyes in his head and in his mind should use them as a guide. Not that I am thereby saying that one should not listen to Aristotle; on the contrary, I applaud his being examined and diligently studied and only blame submitting to him in such a way that one blindly subscribes to all his assertions and accepts them as unquestionable dictates, without searching for other reasons for them. This abuse carries with it another extreme impropriety, namely, that no one makes an effort any longer to try to understand the strength of his demonstrations. Is there anything more shameful in a public discussion [139] dealing with demonstrable conclusions than to see someone slyly appear with a textual passage (often written for some different purpose) and use it to shut the mouth of an opponent? If you want to persist in this manner of studying, lay down the name of philosophers and call yourselves either historians or memory experts, for it is not right that those who never philosophize should usurp the honorable title of philosopher.

However, we should get back to shore in order not to enter an infinite ocean from which we could not get out all day. So, Simplicio, come freely with reasons and demonstrations (yours or Aristotle's) and not with textual passages or mere authorities because our discussions are about the sensible world and not about a world on paper. In yesterday's discussions the earth was drawn out of darkness and brought to light in the open heavens, and we showed that to want to number it among those bodies called heavenly is not so doomed and prostrate a proposition as to be left devoid of any vital energy; and so today we should examine how much probability there is in holding it fixed and completely motionless (referring to the globe as a whole) and how much likelihood there is in making it move with any motion (and if so what type this is). I am undecided about this question, while Simplicio together with Aristotle is firmly on the side of immobility; because of this, he will present step-by-step the motives for their opinion, I will present the answers and arguments for the contrary side, and Sagredo will say what goes on in his mind and to which side he feels drawn.

S
AGR.
    I am happy with this arrangement, but on the condition that I am free to introduce whatever simple common sense may suggest to me.

S
ALV.
    Indeed, I beg you to do exactly that; for I think the various authors have left out few of the easier and (so to speak) cruder considerations, so that only some of the more subtle and esoteric ones may be wanting and lacking; but to investigate these, what subtlety can be more appropriate than that of Sagredo's intellect, which is most acute and penetrating?

S
AGR.
    I may be all that Salviati says, but please, let us not start on another sort of ceremonial digression because right now I am a philosopher and have come to school and not to city hall.

[§8.3 Day II: Diurnal Rotation, Simplicity, and Probability]
¹⁹

S
ALV.
    So let the beginning of our reflections be the following consideration: whatever motion is attributed to the earth, [140] it must remain completely imperceptible and seem nonexisting for us living there and sharing that motion, as long as we look only at terrestrial things; on the other hand, it is equally necessary that the same motion appear to us to be common to all other visible bodies and objects which are separated from the earth and so lack that motion.
²⁰
Thus, the true method of investigating whether any motion may be attributed to the earth and, if so, what kind it may be is to consider and observe whether in the bodies separated from the earth one sees any appearance of motion belonging equally to all; for if a motion were seen, for example, only in the moon and had nothing to do with Venus or Jupiter or other stars, it could not belong to the earth in any way but only to the moon. Now, there is a motion which is very general and most important of all: it is the motion by which the sun, moon, other planets, and fixed stars (in short, the whole universe except only the earth) appear to us to move together from east to west in a period of twenty-four hours. In regard to this first phenomenon, this motion may belong either to the earth only or to the rest of the universe without the earth, for the same appearances would be seen in the one situation as in the other. Aristotle and Ptolemy grasped this consideration, and so when they try to prove the earth to be motionless, they argue only against this diurnal motion; but Aristotle mentions something or other against another motion attributed to it by an ancient author, of which we shall speak in due course.
²¹

S
AGR.
    I understand very well the necessity of which you speak, but I have a difficulty which I do not know how to remove. Copernicus attributed to the earth another motion besides the diurnal one; so by the rule just stated, as regards the appearances, that other motion should remain imperceptible when we look at the earth but be visible in the whole rest of the universe; thus it seems one can necessarily conclude either that he clearly erred in attributing to the earth a motion which does not appear to be general in the heavens, or that if it is general then Ptolemy was equally wrong in not refuting it as he did the other.

[141] S
ALV.
    Your difficulty is a very reasonable one; when we treat of the other motion you will see how much Copernicus' intellect surpassed Ptolemy's in cleverness and profundity, insofar as the former saw what the latter did not, namely, the wonderful accuracy with which this motion is reflected in all other heavenly bodies.
²²
However, for now let us put off this aspect and return to the first point; in regard to this, I shall begin with the more general considerations and propose the reasons that seem to favor the earth's mobility, and then I shall listen to Simplicio for the opposite ones.

Firstly, let us consider the immense size of the stellar sphere in comparison to that of the terrestrial globe, which can fit inside the former many millions of times, and let us also think of the speed required for it to make one entire rotation in twenty-four hours; given these considerations, I cannot persuade myself that anyone can be found who would think it is more reasonable and credible for the celestial sphere to undergo rotation and the terrestrial globe to stand still.

S
AGR.
    Let us assume that all phenomena which may be naturally dependent on these motions are such that the same consequences follow, without a difference, from one supposition as well as the other one; if this were so, my initial and general impression would be that whoever thought it more reasonable to make the whole universe move to keep the earth motionless was more unreasonable than someone who went up to the top of your cathedral to look at the city and its surroundings and demanded that they turn around him so that he would not have to bother turning his head. To overcome this absurdity and revise my impression, thus rendering this supposition more credible than the other one, the advantages deriving from it rather than the other would have to be great and many. But Aristotle, Ptolemy, and Simplicio must think that there are advantages in it; now, if these exist we should be told what they are, or else let it be admitted that there are not or cannot be any.