Chapter 6

As an example of such an attempt I examine the tower argument which the Aristotelians used to refute the motion of the earth. The argument involves natural interpretations - ideas so closely connected with observations that it needs a special effort to realize their existence and to determine their content. Galileo identifies the natural interpretations which are inconsistent with Copernicus and replaces them by others.

It seems to me that (Galileo) suffers greatly from continual digressions, and that he does not stop to explain all that is relevant at each point; which shows that he has not examined them in order, and that he has merely sought reasons for particular effects, without having considered ... first causes ...; and thus that he has built without a foundation. -- DESCARTES

I am (indeed) unwilling to compress philosophical doctrines into the most narrow kind of space and to adopt that stiff, concise and graceless manner, that manner bare of any adornment which pure geometricians call their own, not uttering a single word that has not been given to them by strict necessity ... I do not regard it as a fault to talk about many and diverse things, even in those treatises which have only a single topic ... for I believe that what gives grandeur, nobility, and excellence to our deeds and inventions does not lie in what is necessary - though the absence of it would be a great mistake - but in u hat is not... -- GALILEO

But where common sense believes that rationalizing sophists have the intention of shaking the very fundament of the commonweal,

then it would seem to be not only reasonable, but permissible, and even praiseworthy to aid the good cause with sham reasons rather than leaving the advantage to the ... opponent.

KANT 1

As a concrete illustration and as a basis for further discussion, I shall now briefly describe the manner in which Galileo defused an important counter-argument against the idea of the motion of the earth. I say 'defused', and not 'refuted', because we are dealing with a changing conceptual system as well as with certain attempts at concealment.

According to the argument which convinced Tycho, and which is used against the motion of the earth in Galileo's own Trattato della sfera, observation shows that 'heavy bodies ... falling down from on high, go by a straight and vertical line to the surface of the earth. This is considered an irrefutable argument for the earth being motionless. For, if it made the diurnal rotation, a tower from whose top a rock was let fall, being carried by the whirling of the earth, would travel many hundreds of yards to the east in the time the rock would consume in its fall, and

Descartes' letter is discussed by Salmon as an example of the issue between rationalism and empiricism in 'The Foundations of Scientific Inference', Mind and Cosmos, ed. Colodoy, Pittsburgh, 1966, p. 136. It should rather be regarded as an example of the issue between dogmatic methodologies and opportunistic methodologies, bearing in mind that empiricism can be as strict and unyielding as the most rigorous types of rationalism.

The Kant quotation is from the Critique of Pure Reason, B 777, 8ff (the quotation was brought to my attention by Professor Stanley Rosen's work on Plato's Symposion). Kant continues: 'However, I would think that there is nothing that goes less well together with the intention of asserting a good cause than subterfuge, conceit, and deception. yone could take only this much for granted, then the battle of speculative reason ... would have been concluded long ago, or would soon come to an end. Thus the purity of a cause often stands in the inverse proportion to its truth...' One should also note that Kant explains the rise of civilization on the basis of disingenuous moves which 'have the function to raise mankind above its crude past', op. Cit., 776, 14f. Similar ideas occur in his account of world history.

the rock ought to strike the earth that distance away from the base of the tower.'2

In considering the argument, Galileo at once admits the correctness of the sensory content of the observation made, viz. that 'heavy bodies ... falling from a height, go perpendicularly to the surface of the earth'.3 Considering an author (Chiaramonti) who sets out to convert Copernicans by repeatedly mentioning this fact, he says: 'I wish that this author would not put himself to such trouble trying to have us understand from our senses that this motion of falling bodies is simple straight motion and no other kind, nor get angry and complain because such a clear, obvious, and manifest thing should be called into question. For in this way he hints at believing that to those who say such motion is not straight at all, but rather circular, it seems they see the stone move visibly in an arc, since he calls upon their senses rather than their reason to clarify the effect. This is not the case, Simplicio; for just as I ... have never seen nor ever expect to see, the rock fall any way but perpendicularly, just so do I believe that it appears to the eyes of everyone else. It is, therefore, better to put aside the appearance, on which we all agree, and to use the power of reason either to confirm its reality or to reveal its fallacy.'4 The correctness of the observation is not in question. What is in question is its 'reality' or 'fallacy'. What is meant by this expression ?

The question is answered by an example that occurs in Galileo's next paragraph, 'from which ... one may learn how easily anyone may be deceived by simple appearance, or let us say by the impressions of one's senses. This event is the appearance to those who travel along a street by night of being followed by the moon, with steps equal to theirs, when they see it go gliding along the eaves of the roofs. There it looks to them just as would a cat really running along the tiles and putting them behind it; an appearance which, if reason did not intervene, would only too obviously deceive the senses.'

In this example, we are asked to start with a sensory impression and to consider a statement that is forcefully suggested by it. (The suggestion is so strong that it has led to entire systems of belief and to rituals, as becomes clear from a closer study of the lunar aspects of witchcraft and of other cosmological hypotheses.) Now 'reason intervenes'; the statement suggested by the impression is examined, and one considers other statements in its place. The nature of the impression is not changed a bit by this activity. (This is only approximately true; but we can omit for our present purpose the complications arising from an interaction of impression and proposition.) But it enters new observation statements and plays new, better or worse, parts in our knowledge. What are the reasons and the methods which regulate such exchange ?

To start with, we must become clear about the nature of the total phenomenon: appearance plus statement. There are not two acts - one, noticing a phenomenon; the other, expressing it with the help of the appropriate statement - but only one, viz. saying in a certain observational situation, 'the moon is following me', or, 'the stone is falling straight down'. We may, of course, abstractly subdivide this process into parts, and we may also try to create a situation where statement and phenomenon seem to be psychologically apart and waiting to be related. (This is rather difficult to achieve and is perhaps entirely impossible.) But under normal circumstances such a division does not occur; describing a familiar situation is, for the speaker, an event in which statement and phenomenon are firmly glued together.

This unity is the result of a process of learning that starts in one's childhood. From our very early days we learn to react to situations with the appropriate responses, linguistic or otherwise. The teaching procedures both shape the 'appearance', or 'phenomenon', and establish a firm connection with words, so that finally the phenomena seem to speak for themselves without outside help or extraneous knowledge. They are what the associated statements assert them to be. The language they 'speak' is, of course, influenced by the beliefs of earlier generations which have been held for so long that they no longer appear as separate principles, but enter the terms of everyday discourse, and, after the prescribed training, seem to emerge from the things themselves.

At this point we may want to compare, in our imagination and quite abstractly, the results of the teaching of different languages incorporating different ideologies. We may even want consciously to change some of these ideologies and adapt them to more 'modern' points of view. It is very difficult to say how this will alter our situation, unless we make the further assumption that the quality and structure of sensations (perceptions) or at least the quality and structure of those sensations which enter the body of science, is independent of their linguistic expression. I am very doubtful about even the approximate validity of this assumption, which can be refuted by simple examples, and I am sure that we are depriving ourselves of new and surprising discoveries as long as wc remain within the limits defined by it. Yet, I shall for the moment, remain quite consciously within these limits. (My first task, if I should ever resume writing, would be to explore these limits and to venture beyond them.)

Making the additional simplifying assumption, we can now distinguish between sensations and those 'mental operations which follow so closely upon the senses',5 and which are so firmly connected with their reactions that a separation is difficult to achieve. Considering the origin and the effect of such operations, I shall call them naturul interpretations.

In the history of thought, natural interpretations have been regarded either as a priori presuppositions of science, or else as prejudices which must be removed before any serious examination can begin. The first view is that of Kant, and, in a very different manner and on the basis of very different talents, that of some contemporary linguistic philosophers. The second view is due to Bacon (who had predecessors, however, such as the Greek sceptics).

Galileo is one of those rare thinkers who neither wants forever to retain natural interpretations nor altogether to eliminate them. Wholesale judgements of this kind are quite alien to his way of thinking. He insists upon a critical discussion to decide which natural interpretations can be kept and which must be replaced. This is not always clear from his writings. Quite the contrary. The methods of reminiscence, to which he appeals so freely, are designed to create the impression that nothing has changed and that we continue expressing our observations in old and familiar ways. Yet his attitude is relatively easy to ascertain: natural interpretations are necessary. The senses alone, without the help of reason, cannot give us a true account of nature. What is needed for arriving at such a true account are 'the ... senses, accompanied by reasoning'.6

Moreover, in the arguments dealing with the motion of the earth, it is this reasoning, it is the connotation of the observation terms and not the message of the senses or the appearance that causes trouble. 'It is, therefore, better to put aside the appearance, on which we all agree, and to use the power of reason either to confirm its reality or to reveal its fallacy.'7 Confirming the reality or revealing the fallacy of appearances means, however, examining the validity of those natural interpretations which are so intimately connected with the appearances that we no longer regard them as separate assumptions. I now turn to the first natural interpretation implicit in the argument from falling stones.

According to Copernicus the motion of a falling stone should be 'mixed straight-and-circular'.8 By the 'motion of the stone', is meant not just its motion relative to some visible mark in the visual field of the observer, or its observed motion, but rather its motion in the solar system or in (absolute) space, i.e. its real motion. The familiar facts appealed to in the argument assert a different kind of motion, a simple vertical motion. This result refutes the Copernican hypothesis only if the concept of motion that occurs in the observation statement is the same as the concept of motion that occurs in the Copernican prediction. The observation statement 'the stone is falling straight down' must, therefore, refer to a movement in (absolute) space. It must refer to a real motion.

Now, the force of an 'argument from observation' derives from the fact that the observation statements involved are firmly connected with appearances. There is no use appealing to observation if one does not know how to describe what one sees, or if one can offer one's description with hesitation only, as if one had just learned the language in which it is formulated. Producing an observation statement, then, consists of two very different psychological events: (I) a clear and unambiguous sensation and (2) a clear and unambiguous connection between this sensation and parts of a language. This is the way in which the sensation is made to speak. Do the sensations in the above argument speak the language of real motion?

They speak the language of real motion in the context of 17th-century everyday thought. At least, this is what Galileo tells us. He tells us that the everyday thinking of the time assumes the 'operative' character of all motion, or, to use well-known philosophical terms, it assumes a nail~e realism with respect to motion: except for occasional and unavoidable illusions, apparent motion is identical with real (absolute) motion. Of course, this distinction is not explicitly drawn. One does not first distinguish the apparent motion from the real motion and then connect the two by a correspondence rule. One rather describes, perceives, acts towards motion as if it were already the real thing. Nor does one proceed in this manner under all circumstances. It is admitted that objects may move which are not seen to move; and it is also admitted that certain motions are illusory (cf. the example of the moon mentioned earlier in rhis chapter). Apparent motion and real motion are not always identified. However, there are paradigmatic cases in which it is psychologically very difficult, if not plainly impossible, to admit deception. It is from these paradigmatic cases, and not from the exceptions, that naive realism with respect to motion derives its strength. These are also the situations in which we first learn our kinematic vocabulary. From our very childhood we learn to react to them with concepts which have naive realism built right into them, and which inextricably connect movement and the appearance of movement. The motion of the stone in the tower argument, or the alleged motion of the earth, is such a paradigmatic case. How could one possibly be unaware of the swift motion of a large bulk of matter such as the earth is supposed to be! How could one possibly be unaware of the fact that the falling stone traces a vastly extended trajectory through space! From the point of view of I7thcentury thought and language, the argument is, therefore, impeccable and quite forceful. However, notice how theories ('operative character' of all motion; essential correctness of sense reports) which are not formulated explicitly, enter the debate in the guise of observational terms. We realize again that observational terms are Troian horses which must be watched most carefully. How is one supposed to proceed in such a sticky situation ?

The argument from falling stones seems to refute the Copernican view. This may be due to an inherent disadvantage of Copernicanism; but it may also be due to the presence of natural interpretations which are in need of improvement. The first task, then, is to discover and to isolate these unexamined obstacles to progress.

It was Bacon's belief that natural interpretations could be discovered by a method of analysis that peals them off, one after another, until the sensory core of every observation is laid bare. This method has serious drawbacks. First, natural interpretations of the kind considered by Bacon are not just added to a previously existing field of sensations. They are instrumental in constituting the field, as Bacon says himself. Eliminate all natural interpretations, and you also eliminate the ability to think and to perceive. Second, disregarding this fundamental function of natural interpretations, it should be clear that a person who faces a perceptual field without a single natural interpretation at his disposal would bc completely disoriented, he could not even start the business of science. The fact that we do start, even after some Baconian analysis, therefore shows that the analysis has stopped prematurely. It has stopped at precisely those natural interpretations of which we are not aware and without which we cannot proceed. It follows that the intention to start from scratch, after a complete removal of all natural interpretations, is selfdefeating.

Furthermore, it is not possible even partly to unravel the cluster of natural interpretations. At first sight the task would seem to be simple enough. One takes observation statements, one after the other, and analyses their content. However, concepts that are hidden in observation statements are not likely to reveal themselves in the more abstract parts of language. If they do, it will still be ditlicult to nail them down; concepts, just like percepts, are ambiguous and dependent on background. Moreover, the content of a concept is determined also by the way in which it is related to perception. Yet, how can this way be discovered without circularity ? Perceptions must be identified, and the identifying mechanism will contain some of the very same elements which govern the use of the concept to be investigated. We never penetrate this concept completely, for we always use part of it in the attempt to find its constituents. There is only one way to get out of this circle, and it consists in using an external measure of comparison, including new ways of relating concepts and percepts. Removed from the domain of natural discourse and from all those principles, habits, and attitudes which constitute its form of life, such an external measure will look strange indeed. This, however, is not an argument against its use. On the contrary, such an impression of strangeness reveals that natural interpretations are at work, and it is a first step towards their discovery. Let us explain this situation with the help of the tower example.

The example is intended to show that the Copernican view is not in accordance with 'the facts'. Seen from the point of view of these 'facts', the idea of the motion of the earth is outlandish, absurd, and obviously false, to mention only some of the expressions which were frequently used at the time, and which are still heard whenever professional squares confront a new and counter-factual theory. This makes us suspect that the Copernican view is an external measuring rod of precisely the kind described above.

We can now turn the argument around and use it as a detecting device that helps us to discover the natural interpretations which exclude the motion of the earth. Turning the argument around, we first assert the motion of the earth and then inquire what changes will remove the contradiction. Such an inquiry may take considerable time, and there is a good sense in which it is not finished even today. The contradiction, therefore, may stay with us for decades or even centuries. Still, it must 6e upheld until we have finished our examination or else the examination, the attempt to discover the antediluvian components of our knowledge, cannot even start. This, we have seen, is one of the reasons one can give for retaining, and, perhaps, even for inventing, theories which are inconsistent with the facts. Ideological ingredients of our knowledge and, more especially, of our observations, are discovered with the help of theories which are refuted by them. They are discovered counterinductively.

Let me repeat what has been asserted so far. Theories are tested, and possibly refuted, by facts. Facts contain ideological components, older views which have vanished from sight or were perhaps never formulated in an explicit manner. Such components are highly suspicious. Firstly, because of their age and obscure origin: we do not know why and how they were first introduced; secondly, because their very nature protects them, and always has protected them, from critical examination. In the event of a contradiction between a new and interesting theory and a collection of firmly established facts, the best procedure, therefore, is not to abandon the theory but to use it to discover the hidden principles responsible for the contradiction. Counterinduction is an essential part of such a process of discovery. (Excellent historical example: the arguments against motion and atomicity of Parmenides and Zeno. Diogenes of Sinope, the Cynic, took the simple course that would be taken by many contemporary scientists and all contemporary philosophers: he refuted the arguments by rising and walking up and down. The opposite course, recommended here, has led to much more interesting results, as is witnessed by the history of the case. One should not be too hard on Diogenes, however, for it is also reported that he beat up a pupil who was content with his refutation, exclaiming that he had given reasons which the pupil should not accept without additional reasons of his own.9)

Having discovered a particular natural interpretation, how can we examine it and test it ? Obviously, we cannot proceed in the usual way, i.e. derive predictions and compare them with 'results of observation'. These results are no longer available. The idea that the senses, employed under normal circumstances, produce correct reports of real events, for example reports of the real motion of physical bodies, has now been removed from all observational statements. (Remember that this notion was found to be an essential part of the anti-Copernican argument.) But without it our sensory reactions cease to be relevant for tests. This conclusion has been generalized by some older rationalists, who decided to build their science on reason only and ascribed to observation a quite insignificant auxiliary function. Galileo does not adopt this procedure.

If one natural interpretation causes trouble for an attractive view, and if its elimination removes the view from the domain of observation, then the only acceptable procedure is to use other interpretations and to see what happens. The interpretation which Galileo uses restores the senses to their position as instruments of exploration, but only with respect to the reality of relative motion. Motion 'among things which share it in common' is 'non-operative', that is, 'it remains insensible, imperceptible, and without any effect whatever'.10 Galileo's first step, in his joint examination of the Copernican doctrine and of a familiar but hidden natural interpretation, consists therefore in replacing the latter by a different interpretation. In other words, he introduces a new observation language.

This is, of course, an entirely legitimate move. In general, the observation language which enters an argument has been in use for a long time and is quite familiar. Considering the structure of common idioms on the one hand, and of the Aristotelian philosophy on the other, neither this use nor this familiarity can be regarded as a test of the underlying principles. These principles, these natural interpretations, occur in every description. Extraordinary cases which might create difficulties are defused with the help of 'adjustor words',ll such as 'like' or 'analogous', which divert them so that the basic ontology remains unchallenged. A test is, however, urgently needed. It is especially needed in those cases where the principles seem to threaten a new theory. It is then quite reasonable to introduce alternative observation languages and to compare them both with the original idiom and with the theory under examination.

not act and is as if it did not exist' (p. TT6); 'Whatever motion comes to be attributed to the earth must necessarily remain imperceptible ... so long as we look only at terrestrial objects' (p. TT4); '... motion that is common to many moving things is idle and inconsequential to the relation of those movables among themselves...' (p. TT6). On the other hand, (2) he also suggests that 'nothing ... moves ~n a stra~ght hne by nature. The motion of all celestial objects is in a circle; ships, coaches horses birds, all move in a circle around the earth; the motions of the parts of animals are ali circular; in sum - we are forced to assume that only gravia leorsum and lev~a sursum move apparently in a straight line; but even that is not certain as long as it has not been proven that the earth is at rest' (p. T9). Now, if (2) is adopted, then the loose parts of systems moving in a straight line will tend to describe circular paths, thus contradicting (I). It is this inconsistency which has prompted me to split Galileo's argument into two steps, one dealing with the relativity of motion (only relative motion ~s not~ced ), the other dealing with inertial laws (and only inertial motion leaves the relatson between the parts of a system unaffected - assuming, of course, that neighbouring inertial motions are approximately parallel). For the two steps of the argument, see the next chapter. One must also realize that accepting relativity of motion even for inertial paths, means giving up the impetus theory. This Galileo seems to have done by now, for his argument for the existence of 'boundless' or 'perpetual' motions which he outlines on pp. T47ff of the D'alogue appeals to motions which are neutral, i.e. neither natural nor forced, and which may therefore ( ?) be assumed to go on for ever

Proceeding in this way, we must make sure that the comparison is fair. That is, we must not criticize an idiom that is supposed to function as an observation language because it is not yet well known and is, therefore, less strongly connected with our sensory reactions and less plausible than is another, more 'common' idiom. Superficial criticisms of this kind, which have been elevated into an entire new 'philosophy' abound in discussions of the mind-body problem. Philosophers who want to introduce and to test new views thus find themselves faced not with arguments, which they could most likely answer, but with an impenetrable stone wall of well-entrenched reactions. This is not at all different from the attitude of people ignorant of foreign languages, who feel that a certain colour is much better described by 'red' than by 'rosso'. As opposed to such attempts at conversion by appeal to familiarity ('I know what pains are, and I also know, from introspection, that they have nothing whatever to do with material processes!'), we must emphasize that a comparative judgement of observation languages, e.g. materialistic observation languages, phenomenalistic observation languages, objectiveidealistic observation languages, theological observation languages, etc., can start only when all of them are spoken equally fluently.

Let us now continue with our analysis of Galileo's reasoning.

Notes

1. The three quotations are: Descartes, letter to Mersenne of II October 1638, Oeuvres, II, p. 380. Galileo, letter to Leopold of Toscana of 1640, usually quoted under the title Sul Candor Lunare, Edizione Nazionale, VIII, p. 491. For a detailed discussion of Galileo's style and its connection with his natural philosophy c# L. Olschki, Galileo und seine Zeit: Geschichte der neusprachlichen wissenschaftlicha~ Litaatur, Vol. III, Halle, 1927, reprinted Vaduz, 1965. The letter to Leopold is quoted and discussed on pp. 455ff.

2. Dialogue, op. Cit., p. IZ6.

3. ibid., p. IZS.

4. ibid., p. Z56.

5. Francis Bacon, Novam Organum, Introduction.

6. Dialogue, op. cit., p. 255, my italics.

7. ibid., p. 256.

8. ibid., p. 248.

9. Hegel, Vorlesungen uber die Gesehichte der Philosophie, I, ed. C. L. Michelet, Berlin, T840, p. 289.

10. Dialogue, op. cit., p. 171. Galileo's kinematic relativism is not consistent. In the passage quoted, he proposes the view (I) that shared motion has no effect whatsoever. 'Motion,' he says, 'in so far as it is and acts as motion, to that extent exists relatively to things that lack it; and among things which all share equally in any motion, it does

11. J. L. Austin, Sense and Sensib~ha, New York, T964, p. 74. Adjustor words play an important role in the Aristotelian philosophy.

Chapter 7

The new natural interpretations constitute a new and highly abstract observation language. They are introduced and concealed so that one fails to notice the change that has taken place (method of anamnesis). They contain the idea of the relativity of all motion and the law of circular inertia.

Galileo replaces one natural interpretation by a very different and as yet (1630) at least partly unnatural interpretation. How does he proceed ? How does he manage to introduce absurd and counterinductive assertions, such as the assertion that the earth moves, and yet get them a just and attentive hearing ? One anticipates that arguments will not suffice -an interesting and highly important limitation of rationalism - and Galileo's utterances are indeed arguments in appearance only. For Galileo uses propaganda. He uses psychological tricks in addition to whatever intellectual reasons he has to offer. These tricks are very successful: they lead him to victory. But they obscure the new attitude towards experience that is in the making, and postpone for centuries the possibility of a reasonable philosophy. They obscure the fact that the experience on which Galileo wants to base the Copernican view is nothing but the result of his own fertile imagination, that it has been in:,ented. They obscure this fact by insinuating that the new results which emerge are known and conceded by all, and need only be called to our attention to appear as the most obvious expression of the truth.

Galileo 'reminds' us that there are situations in which the nonoperative character of shared motion is just as evident and as firmly believed as the idea of the operative character of all motion is in other circumstances. (This latter idea is, therefore, not the only natural interpretation of motion.) The situations are: events in a boat, in a smoothly moving carriage, and in other systems that contain an observer and permit him to carry out some simple operations.

'Sagredo: There has just occurred to me a certain fantasy which passed through my imagination one day while I was sailing to Aleppo, where I was going as consul for our country.... If the point of a pen had been on the ship during my whole voyage from Venice to Alexandretta and had had the property of leaving visible marks of its whole trip, what trace - what mark - what line would it have left ?

Simplicio: It would have left a line extending from Venice to there; not perfectly straight - or rather, not Iying in the perfect arc of a circle -but more or less fluctuating according as the vessel would now and again have rocked. But this bending in some places a yard or two to the right or left, up or down, in length of many hundreds of miles, would have made little alteration in the whole extent of the line. These would scarcely be sensible, and, without an error of any moment, it could be called part of a perfect arc.

Sagredo: So that if the fluctuation of the waves were taken away and the motion of the vessel were calm and tranquil, the true and precise motion of that pen point would have been an arc of a perfect circle. Now if I had had that same pen continually in my hand, and had moved it only a little sometimes this way or that, what alterations should I have brought into the main extent of this line ?

Simplicio: Less than that which would be given to a straight line a thousand yards long which deviated from absolute straightness here and there by a flea's eye.

Sagredo: Then if an artist had begun drawing with that pen on a sheet of paper when he left the port and had continued doing so all the way to Alexandretta, he would have been able to derive from the pen's motion a whole narrative of many figures, completely traced and sketched in thousands of directions, with landscapes, buildings, animals, and other things. Yet the actual real essential movement marked by the pen point would have been only a line; long, indeed, but very simple. But as to the artist's own actions, these would have been conducted exactly the same as if the ship had been standing still. The reason that of the pen's long motion no trace would remain except the marks drawn upon the paper is that the gross motion from Venice to Alexandretta was common to the paper, the pen, and everything else in the ship. But the small motions back and forth, to right and left, communicated by the artist's fingers to the pen but not to the paper, and belonging to the former alone, could thereby leave a trace on the paper which remained stationary to those motions.'1

Or

'Salviati: ... imagine yourself in a boat with your eyes fixed on a point of the sail yard. Do you think that because the boat is moving along briskly, you will have to move your eyes in order to keep your vision always on that point of the sail yard and follow its motion ?

Simplicio: I am sure that I should not need to make any change at all; not just as to my vision, but if I had aimed a musket I should never have to move it a hairsbreadth to keep it aimed, no matter how the boat moved.

Salviati: And this comes about because the motion which the ship confers upon the sail yard, it confers also upon you and upon your eyes, so that you need not move them a bit in order to gaze at the top of the sail yard, which consequently appears motionless to you. (And the rays of vision go from the eye to the sail yard just as if a cord were tied between the two ends of the boat. Now a hundred cords are tied at different fixed points, each of which keeps its place whether the ship moves or remains still.)'2

It is clear that these situations lead to a non-operative concept of motion even within common sense.

On the other hand, common sense, and I mean 17th-century Italianartisan common sense, also contains the idea of the operative character of all motion. This latter idea arises when a limited object that does not contain too many parts moves in vast and stable surroundings; for example, when a camel trots through the desert, or when a stone descends from a tower.

Now Galileo urges us to 'remember' the conditions in which we assert the non-operative character of shared motion in this case also, and to subsume the second case under the first.

Thus, the first of the two paradigms of non-operative motion mentioned above is followed by the assertion that - 'It is likewise true that the earth being moved, the motion of the stone in descending is actually a long stretch of many hundred yards, or even many thousand; and had it been able to mark its course in motionless air or upon some other surface, it would have left a very long slanting line. But that part of all this motion which is common to the rock, the tower, and ourselves remains insensible and as if it did not exist. Thcre remains observable only that part in which neither the tower nor we are participants; in a word, that with which the stone, in falling, measures the tower.'3

And the second paradigm precedes the exhortation to 'transfer this argument to the whirling of the earth and to the rock placed on top of the tower, whose motion you cannot discern because, in common with the rock, you possess from the earth that motion which is required for following the tower; you do not need to move your eyes. Next, if you add to the rock a downward motion which is peculiar to it and not shared by you, and which is mixed with this circular motion, the circular portion of the motion which is common to the stone and the eye continues to be imperceptible. The straight motion alone is sensible, for to follow that you must move your eyes downwards.'4

This is strong persuasion indeed.

Yielding to this persuasion, we now quite automatically start confounding the conditions of the two cases and become relativists. This is the essence of Galileo's trickery! As a result, the clash between Copernicus and 'the conditions affecting ourselves and those in the air above US'5 dissolves into thin air, and we finally realize 'that all terrestrial events from which it is ordinarily held that the earth stands still and the sun and the fixed stars are moving would necessarily appear just the same to us if the earth moved and the other stood still'.6

Let us now look at the situation from a more abstract point of view. We start ~ith two conceptual sub-systems of 'ordinary' thought (see the following table). One of them regards motion as an absolute process which always has effects, effects on our senses included. The description of this conceptual system given here may be somewhat idealized; but the arguments of Copernicus' opponents which are quoted by Galileo himself and, according to him, are 'very plausible',7 show that there was a widespread tendency to think in its terms, and that this tendency was a serious obstacle to the discussion of alternative ideas. Occasionally, one finds even more primitive ways of thinking, where concepts such as 'up' and 'down' are used absolutely. Examples are: the assertion 'that the earth is too heavy to climb up over the sun and then fall headlong back down again',8 or the assertion that 'after a short time the mountains, sinking downward with the rotation of the terrestrial globe, would get into such a position that whereas a little earlier one would have had to climb steeply to their peaks, a few hours later one would have to stoop

Crew and Alfonso de Salvio, New York, T958, p. 164: 'The same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.' Professor McMullin, in a critique of this way of seeing things, wants more 'logical and biographical just)fication' for my assertion that Galileo not only argued, but also cheated ['A Taxonomy of the Relation between History and Philosophy of Science', htinnesota Stud~cs, Vol. 5, Minneapolis, I97I, p. 39], and he objects to the way in which I let Galileo introduce dynamical relativism. According to him 'what Galileo argues is that since his opponent already interprets observations made in such a context [movements on boats] in a 'relativistic' way, how can he consistently do otherwise in the case of observations made on the earth's surface ?' (op. cit., p. 40). This is indeed how Galileo argues. But he argues so against an opponent who, according to him, 'feels a great repugnance towards recognizing this non-operative quality of motion among the things which share it in common' (Dialogue, op. cit., p. I7I), who is convinced that a boat, apart from having relative motions, has absolute positions and motions as ~Dell (cf. Aristotle, Physics, 208b8ff), and who at any rate has developed the art of using different notions on different occasions without running into a contradiction. Now if this is the position to be attacked, then showing that an opponent has a relative idea of motion, or frequently uses the relative idea in his everyday affairs, is not at all 'proof of inconsistency in his own "paradigm" ' (McMullin, op. cit., p. 4o). It just reveals one part of that paradigm without touching the other. The argument turns into the desired proof only if the absolute notion is either suppressed or spirited away, or else identified with the relativistic notion - and this is what Galileo actually does, though surreptitiously, as I have tried to show. and descend in order to get there'.9 Galileo, in his marginal notes, calls these 'utterly childish reasons [which] sufficed to keep imbeciles believing in the fixity of the earth',10 and he thinks it unnecessary 'to bother about such men as those, whose name is legion, or to take notice of their fooleries'.1l Yet it is clear that the absolute idea of motion was 'wellentrenched', and that the attempt to replace it was bound to encounter strong resistance.l2

The second conceptual system is built around the relativity of motion, and is also well-entrenched in its own domain of application. Galileo aims at replacing the first system by the second in all cases, terrestrial as well as celestial. Naive realism with respect to motion is to be completely eliminated.

PARADIGM I: Motion of compact objects in stable surroundings of great spatial extension - deer observed by the hunter.

PARADIGM II: Motion of objects in boats, coaches and other moving systems.

Natural interpretation: All motion is operative.

Natural interpretation: Only relative motion is operative.

Falling stone Motion of earth prores predicts

Earth at rest Oblique motion of stone

Falling stone Motion of earth

prores predicts

No relatite motion between starting point and earth

No relative motion between starting point and stone

Now, we have seen that this naive realism is on occasions an essential part of our observational vocabulary. On these occasions (Paradigm b, the observation language contains the idea of the efficacy of all motion. Or, to express it in the material mode of speech, our experience in these situations is an experience of objects which move absolutely. Taking this into consideration, it is apparent that Galileo's proposal amounts to a partial revision of our observation language or of our experience. An experience which partly contradicts the idea of the motion of the earth is turned into an experience that confirms it, at least as far as 'terrestrial things' are concerned.13 This is what actually happens. But Galileo wants to persuade us that no change has taken place, that the second conceptual system is already universally knoa~n, even though it is not universally used. Salviati, his representative in the Dialogue, his opponent Simplicio and Sagredo the intelligent layman, all connect Galileo's method of argumentation with Plato's theory of anamnesis - a clever tactical move, typically Galilean one is inclined to say. Yet we must not allow ourselves to be deceived about the revolutionary development that is actually taking place.

The resistance against the assumption that shared motion is nonoperative was equated with the resistance which forgotten ideas exhibit towards the attempt to make them known. Let us accept this interpretation of the resistance! But let us not forget its existenre. We must then admit that it restricts the use of the relativistic ideas, confining them to part of our everyday experience. Outside this part, i.e. in interplanetary space, they are 'forgotten' and therefore not active. But outside this part there is not complete chaos. Other concepts are used, among them whose very same absolutistic concepts which derive from the first paradigm. We not only use them, but we must admit that they are entirely adequate. No difficulties arise as long as one remains within the limits of the first paradigm. 'Experience', i.e. the totality of all facts from all domains, cannot force us to carry out the change which Galileo wants to introduce. The motive for a change must come from a different source.

It comes, first, from the desire to see 'the whole [correspond] to its parts with wonderful simplicity',l4 as Copernicus had already expressed himself. It comes from the 'typically metaphysical urge' for unity of understanding and conceptual presentation. And the motive for a change is connected, secondly, with the intention to make room for the motion of the earth, which Galileo accepts and is not prepared to give up. The idea of the motion of the earth is closer to the first paradigm than to the second, or at least it was at the time of Galileo. This gave strength to the Aristotelian arguments, and made them plausible. To eliminate this plausibility, it was necessary to subsume the first paradigm under the second, and to extend the relative notions to all phenomena. The idea of anamnesis functions here as a psychological crutch, as a lever which smooths the process of subsumption by concealing its existence. As a result we are now ready to apply the relative notions not only to boats, coaches, birds, but to the 'solid and well-established earth' as a whole. And we have the impression that this readiness was in us all the time, although it took some effort to make it conscious. ~I'his impression is most certainly erroneous: it is the result of Galileo's propagandistic machinations. We would do better to describe the situation in a different way, as a change of our conceptual system. Or, because we are dealing with concepts which belong to natural interpretations, and which are therefore connected uith sensations in a very direct way, we should describe it as a change of experienre that allous us to accommodate the Copernican doctrine. The change corresponds perfectly to the pattern described in Chapter I! belou: an inadequate view, the Copernican theory, is supported by another inadequate view, the idea of the nonoperative character of shared motion, and both theories gain strength and give support to each other in the process. It is this change which underlies the transition from the Aristotelian point of view to the epistemology of modern science.

For experience now ceases to be the unchangeable fundament which it is both in common sense and in the Aristotelian philosophy. The attempt to support Copernicus makes experience 'fluid' in the very same manner in which it makes the heavens fluid, 'so that each star roves around in it by itself'.l5 An empiricist who starts from experience, and builds on it without ever looking back, now loses the very ground on which he stands. Neither the earth, 'the solid, well-established earth', nor the facts on which he usually relies can be trusted any longer. It is clear that a F)hilosophy that uses such a fluid and changing experience needs new methodological principles which do not insist on an asymmetric judgement of theories by experience. Classical ph,!sics intuitively adopts such principles; at least the great and independent thinkers, such as Newton, Faraday, Boltzmann proceed in this way. But its oDaicial doctrine still clings to the idea of a stable and unchanging basis. The clash between this doctrine and the actual procedure is concealed by a tendentious presentation of the r esults of research that hides their revolutionary origin and suggests that they arose from a stable and unchanging source. These methods of concealment start with Galileo's attempt to introduce new ideas under the cover of anamnesis, and they culminate in Newton.16 They must be exposed if we want to arrive at a better account of the progressive elements in science.

My discussion of the anti-Copernican argument is not yet complete. So far, I have tried to discover what assumption will make a stone that moves alongside a moring toTDer appear to fall 'straight down', instead of being seen to move in an arc. The assumption, which I shall call the relativ~ity principle, that our senses notice only relative motion and are completely insensitive to a motion which objects have in common, was seen to do the trick. What remains to be explained is 7Dhy the stone stays with the tower and is not left behind. In order to save the Copernican view, one must explain not only why a motion that preserves the relation among visible objects remains unnoticed, but also, why a common motion of various objects does not affect their relation. That is, one must explain why such a motion is not a causal agent. Turning the question around in the manner explained in text to footnote ~o, page 78 of the last chapter, it is now apparent that the anti-Copernican argument described there rests on two natural interpretations: viz., the epistemological assumption that absolute motion is always noticed, and the dynamical principle that objects (such as the falling stone) which are not interfered with assume their natural motion. The present problem is to supplement the relativity principle with a new law of inertia in such a fashion that the motion of the earth can still be asserted. One sees at once that the following law, the principle of circular inertia as I shall call it, provides the required solution: an object that moves with a given angular velocity on a frictionless sphere around the centre of the earth will continue moving with the same angular velocity forever. Combining the appearance of the falling stone with the relativity principle, the principle of circular inertia and with some simple assumptions concerning the composition of velocities,'7 we obtain an argument which no longer endangers Copernicus' view, but can be used to give it partial support.

The relativity principle was defended in two ways. The first was by showing how it helps Copernicus: this defence is truly ad hoc. The second was by pointing to its function in common sense, and by surreptitiously generalizing that function (see above). No independent argument was given for its validity. Galileo's support for the principle of circular inertia is of exactly the same kind. He introduces the principle, again not by reference to experiment or to independent observation, but by reference to what everyone is already supposed to know.

Simplicio: So you have not made a hundred tests, or even one ? And yet you so freely declare it to be certain ? ...

Salviati: Without experiment, I am sure that the effect will happen as I tell you, because it must happen that way; and I might add that you yourself also know that it cannot happen otherwise, no matter how you may pretend not to know it.... But I am so handy at picking people's brains that I shall make you confess this in spite of yourself.'l8

Step by step, Simplicio is forced to admit that a body that moves, without friction, on a sphere concentric with the centre of the earth will carry out a 'boundless', a 'perpetual' motion. We know, of course, especially after the analysis we have just completed of the non-operative character of shared motion, that what Simplicio accepts is based neither on experiment nor on corroborated theory. It is a daring new suggestion involving a tremendous leap of the imagination. A little more analysis then shows that this suggestion is connected with experiments, such as the 'experiments' of the Discorsi,19 by ad hoc hypotheses. (The amount falling from the mast of a ship while it is in motion....' Earlier, p. I j4, it is implied rather than observed, that the stone will fall to the foot of the mast, even if the ship should be in motion while a possible experiment is discussed on p. T86 Bruno (La Ccna de le Ceneri, Opere Italiane, I, ed. Giovanni Gentile, Bari, 1907, p. 83) takes it for granted that the stone will arrive at the foot of the mast. It should be noted that the problem did not readily lend itself to an experimental solution. Experiments were made, but their results were far from conclusive. Cf. A. Armitage, 'The Deviation of Falling Bodies', Annals of Scicnce, 5, I94I-7, pp. 342ff, and A. Koyre, Metaphysics and Measurement, Cambridge, 1968, pp. 8gff. The tower argument can be found in Aristotle, De Coelo, 2g6b22, and Ptolemy, Syntaxis, i, 8. Copernicus discusses it in the same chapter of De Revol., but tries to defuse it in the next chapter (cf. footnote IZ to Chapter 8 of the present essay). Its role in the middle ages is described in M. Clagett, The Science of Meehanics in the Middle Ages, Madison, 1959, Chapter ~o.

Notes

1. Dialogue, op. cit., pp. 17 rff.

2. ibid., pp. 249ff. That phenomena of seen motion depend on relative motion has been asserted by Euclid in his Optics, Theon red. par. 4gff. An old scholion of par. 50 uses the example of a boat leaving the harbour: Heiberg, vii, ~83. The example is repeated by Copernicus in Book I, Chapter viii, of De Revol. It was a commonplace in mediaeval optics. Cf Witelo, Perspectiva, iv, par. 138 (Baser, 157Z, p. 180). We know now that it is valid for constant velocities only.

3. ibid., pp. 172ff.

4. ibid., p. 250.

5. Ptolemy, Syntaxis, i, T, p. 7.

6. Dialogue, p. 416: cf. the Dialogacs Concerning Two New Sciences, transl. Henry

7. Dialogue, op. cit., p. ~31.

8. ibid., p. 3z7.

9. ibid., p. 330.

1O. ibid., p. 327.

11. ibid, p. 3z7, italics added.

12. The idea that there is an absolute direction in the universe has a very interesting history. It rests on the structure of ~e gravita_~onal field on the surface of the earth, or of that part of the earth which the observer knows, and generalizes the expenences made ~ere. The generalization is only rarely regarded as a separate hypothesis, it ra~er enters the 'grammar' of comTnon sense and gives the terms 'up' and 'down' an absolute mean~ng. (This is a 'natural interpreta_ion', in precisely the sense that was explained in the text above.) Lactan_ius, a church father of the fourth cenulry, appeals to this meaning when he asks (Div~nac Institutiones, III, De Falsa Sapientia): 'Is one really going to be so confused as to assume the existence of humans whose feet are above their heads ? Where trees and fruit grow not upwards, but downwards ?' The same use of language is presupposed by that 'mass of untutored men' who raise the ques_ion why the antipodeans are not falling off the earth (Pliny, Natural History, II, pp. I6I~; cf. also Ptolemy, Syntaxis, I, 7). The attempts of Thales, Anaximenes and Xenophanes to find support for the earth which prevents it from falling 'down' (Anstotle, De Coelo, ~g4a~ff) shows that almost all early philosophers, with the sole exception of Anaximander, shared in this way of thinking. (For the Atornists, who assume that the atoms onginally fall 'down', cf. Jammer, Concepts of Space, Cambridge, Mass., 1953, p. II.) Even Galileo, who thoroughly ridicules the idea of the falling ant~podes (Dialogue, op. cit., p. 331), occasionally speaks of the 'upper half of the moon', meaning that part of the moon 'which is invisible to us'. And let us not forget that some linguis_ic phil~ sophers of today 'who are too stupid to recognizc their own limitations' (Galileo, op. cit., p. 3~7) want to revive the absolute meaning of 'up-down' et least locally. Thus the power over the minds of his contemporanes of a pn~utive conceptual frame, assunung an anisotropic world, which Galileo had also to fight, must not be underestimated. For an exanuna_~on of some aspects of British common sense at the time of Galileo, including astronomical common sense, see E. M. W. Tillyard, The Elizabethan World Picture, London, 1963. The agreement between popular opinion and the centrally symmetric universe is frequently asserted by Aristotle, e.g. in De Coelo, p. 308a23f.

13. Dialogue, Op. Cit., pp. I32 and 4T6.

14. ibid., p. 34r. Galileo quotes here from Copernicus' address to Pope Paul III in De Revolutioniljus; cf. also Chapter lo and the -Varratio Prima (quoted from E. Rosen, Three Copernican Treatises, New York, ~959, p. 165): 'For all these phenomena appear to be linked most nobly together, as by a golden chain; and each of the planets, by its position, and order, and every inequality of its motion, bears witness that the earth moves and that we who dwell upon the globe of the earth, instead of accepting its changes of position, believe that the planets wander in all sorts of motions of their own.' Note that empirical reasons are absent from the argument and have to be, for Copernicus himself admits (Commentariolus, op. cit., p. 57) that the Ptolemaic theory is 'consistent with the numerical data'.

15. Dialogue, op. cit., p. ~20.

16. 'aassical Empiricism', op. cit.

17. These assumptions were not at all a matter of course, but conflicted with some very basic ideas of Aristotelian physics.

18. Dialogue, Op. Cit., p. 147.

19. 1nclaenm~y, many ot tne experiences' or 'experiments' used in the arguments about the motion of the earth are entirely fictitious. Thus Galileo, in his Trattato della Sfera (Edizione,Vazionale, Vol. II, pp. 2IIff), which 'follows the opinion of Aristotle and of Ptolemy' (p. 223), uses this argument against a rotation of the earth: '... objects which one lets fall from high places to the ground such as a stone from the top of a tower would not fall towards the foot of that tower; for during the time which the stone coming rectilinearly towards the ground, spends in the air, the earth, escaping it, and moving towards the east would receive it in a part far removed from the foot of the tower in exactly the same manner ~n which a stone that is droppelfrom the mast of a rapidly moving skip will not fall towards its foot, but more towards the stern' (p. 224). The italicized reference to the behaviour of stones on ships is again used in the Dialogue (p. 126), when the Ptolemaic arguments are discussed, but it is no longer accepted as correct. 'It seems to be an appropriate time,' says Salviati (ibid., p. 180), 'to take notice of a certain generosity on the part of the Copernicans towards their adversaries when with perhaps too much liberality, they concede as true and correct a number of experiments which their opponents have never made. Such for example is that of the body of friction to be eliminated follows not from independent investigations -such investigations commence only much later, in the I8th century- but from the result to be achieved, viz. the circular law of inertia.) Viewing natural phenomena in this way leads to a re-evaluation of all experience, as we have seen. We can now add that it leads to the invention of a new kind of experience that is not only more sophisticated hut also far more speculative than is the experience of Aristotle or of common sense. Speaking paradoxically, but not incorrectly, one may say that Galileo invents an experience that has metaphysical ingredients. It is by means of such an experience that the transition from a geostatic cosmology to the point of view of Copernicus and Kepler is achieved.