Aristotle finds in the human ‘ mind,’ which has faculties not granied to the highest of the brutes, a xlvi INTRODUCTION power to isolate in thought what is never isolated in fact, analogous to the necessary action of a special sense in isolating to the experience of the conscious- ness what is never isolated in the challenge of the abject. This is the power of ‘ abstraction’ by which we can think apart of that which never exists apart, The cye enables—nay, compels us—to ‘abstract’ or draw away from all coloured things a vast range and variety of impressions which all have, anid their differences, a something in common, distinguishing them as a group from all other im- pressions. The word ‘colour’ is the record of this sense-abstraction. All names, or ‘ nouns,’ are in like manner records of spontaneous ‘ abstractions,’ from concrete individual examples, of something that exists in all the individuals to which the name ἘΡΒΝ ΕΗ but never by itsclf in separation from them all.
But ‘ colour ᾿ is the name of a group of sensations, and its isolation from other groups is done for us by our senses. In the mental world we must learn to isolate in thought likenesses or identities of which there is no sense-register, and which are never found in fact or experience isolated from unlikenesses and diversities, If we can do this we shall have found the realm of abiding realities and shall ‘ understand,’ so far as man can understand, what it is, in virtue of which beautiful things are beautiful, living things alive, convincing arguments convincing, and all the rest. We shall then command a realm of abiding truth, but we shall find it not outside and above the change and flux of things and experiences but at their very heart, separable from them in thought but never in xlvit INTRODUCTION reality. Such ‘abstractions ” exist, apart and sejunet from ‘ concrete ’ things and beings only conceptually; but their existence in existing things and experiences js as real as those things and experiences themselves, and it is only by isolating or abstracting the con- ceptual that we can have any grasp of the permanent and unchanging amidst the flux and change of sense- experiences, which we mean by true ‘ knowledge’ as distinct from cognitive familiarity.
This is Avistotle’s solution of the old problem as to where we are to find the permanent and changeless when we have no direct access to anything but the evanescent and varying. He places it in sharp contrast to the Platonic doctrine of Ideas; and in his first attempt to arrest and define it before he has ained the complete mastery of it to which he ultimately attained, we catch him in one of those rare moments in which pure intellect kindles on his lips into passion as he feels himself to be in the very act of bringing the unceasing flux under the control of an intelligible order——like one who has arrested the rout of a bewildered and panic-stricken army and is rallying and inspiring it for victory.* Thus Aristotle died, as he had lived, a passionate Platonist, under the abiding illusion that he was building up on his own rational basis of abstraction a complete reinforcement of his beloved master’s teaching, and letting himself go straight for the central truth which his master never approached directly, but always in some oblique manner. So his love burned undimmed and steady, though to us 4 [In Anal. Post. ii. 19, 100 a 11, Aristotle uses this image to illustrate the power of the mind to pass from particulars to universals.—C.]
xiviii INTRODUCTION he seems to be always attacking the doctrine of Ideas, which he held to be superfluous irrelevancies, and always fretting against certain misunderstood passages in Plato’s Timaeus, of which indeed there does not appear to be any real explanation—there are only hints—but Aristotle thought he understood them and rejected them, With this clue in his hand Aristotle examines language, the treasure-house and record-office of all the spontaneous activities of the faculty of ‘ abstrac- tion ’ that has not yet recognized itself. There are ‘kinds ’ of words, as well as words: verb and noun, for instance. What is it exactly in which all verbs are alike each other and unlike nouns? And what is the difference between words, which merely present something to our minds, and sentences, which perhaps assert connexions between things (Grammar)? And what are the ‘ kinds’ of assertion we can make? What is the difference between telling what a thing is, and telling what qualities it has, or how much of it there is, or in what position it is, or in what relations to other things? Is it possible to make an exhaustive list of possible kinds of assertion, to one and only one of which every assertion must belong (the Categories)? In such inquiries we are trying to isolate in thonght some function or characteristic of a group of words or pro- positions; the characteristic, namely, which makes them what they are, and enables us to understand why they are a group, which is indeed the very essence and truth of their being, but which never and nowhere exists except in them, and in them is never objectively isolated.
xlix INTRODUCTION 3. The Categories This brings us to the crucial distinction between the aestheta and the ποδία in Greek, the sensibilia and the intelligibilia in Latin, the concrete and the abstract οὐ the particular and the general in English.
But unfortunately the English terms do not adequately emphasize the point that a concrete and ‘ particular ’ stone or tree, for instance, is perceived by the senses as having an objective existence of its own, whereas the ‘ generals,’ that is to say the intrinsic characteristics that constitute stones or trees as distinguishable groups or classes of things, while existing in and to the intelligence in separation from the ‘ particulars,’ have no objective existence except in them. These ‘generals,’ then, are ab- stracted oy ‘ drawn off’ from the concrete and parti- cularized individuals by the intelligence, and, as contemplated apart from the particulars, exist only in and to the intelligence.
The contrast would be well marked by ‘ sensible’ and ‘intelligible,’ if the words were free enough from other associations to be safe depositories of the meanings: ‘ accessible to cognition by the senses,’ and ‘accessible to cognition by the intelligence’; and perhaps with due precautions we may be able sometimes to speak of the concrete objects of sense- perception simply as ‘sensible’; but for ‘ in- telligible’ we shall have to substitute the word ‘conceptual.’ It is harsh and, though true, not very illuminating, to say that the objects of sense are ‘ unintelligible,’ but not harsh to say that they are ‘not conceptual.’ It is quite misleading to say ] INTRODUCTION {as you may in Latin) that we can only reach the intelligible through the unintelligible, but to say that we can only reach the conceptual by distilling, sublimating, or ‘abstracting’ it from the non- conceptual and concrete, that is to say from the ‘ sensible,’ is (it may be hoped) illuminating.
Let it be understood, then, that ‘ the conceptual ’ (and sometimes ‘ a concept ’) is to represent the Latin intelligibile and the Greek noéion. Jt is no more than a variant of ‘ abstract,’ which stresses the fact that the abstract exists objectively nowhere but in the conerete, and also that it is only (according to Aristotle) from the concrete that the intelligence can draw it off.
We can now go forward with more rapid steps. * Abstraction’ consists in grouping, and we may group the concrete sensibles with which we start as our primary data just according to our convenience or fancy; but the ‘ common nouns’ of our language are the registcr of a series of spontaneous abstrac- tions and groupings which have established them- selves as serviceable. Science attempts to system- atize these groupings, to give them precision, to fill in gaps, and so forth; but wherever there are common nouns, there are ready-made ‘ generals,’ ‘ abstrac- tions,’ or ‘ concepts’; for language is a deposit and a reservoir of thought.
The simplest illustrations may be drawn from the consideration of such a scale as this: ‘ horses’ and ‘men’ are two groups included in the wider group of ‘ animals’; animals and plants are two groups included in the wider group of ‘living organism’; living organisms and inorganic substances are two groups included in the wider group of ‘ material hi INTRODUCTION entities.’ Is there any yet higher group which includes material entities and some other group?
The attempt to answer this question will take us deep into the heart of our subject, but before embarking upon it we may note that it is usual to call any group a genus with respect to the groups it includes, and a species with reference to the genus that includes it. Thus, ‘ animal’ would stand in our illustrative scale for the genus of which * horse * and ‘man’ are species, and for a species of the genus ‘ vital organism,’ Our question then is: Do ‘ material entities ’ constitute a supreme genus which cannot be ranked as a species under any genus wider than itself?
If we take ‘material entity ’’ to mean anything that the senses, and pre-eminently the common sense, announce to us as existing objectively, in- dependently of our knowledge or perception of it, but distinguishable by us from other things like or unlike itself, then we shall say that such ἡ entities,’ perceived by the common sense, are always concrete. A substance such as air, or a stone, a tree, a man, are concrete substances, things, or beings, revealed (the metaphysical inadequacy of all this range of conceptions has been sufficiently emphasized) to us by the senses as existing both in themselves and independently of our cognitions. But the colour, weight, size, or extension of these things, even if announced by the senses, is not revealed to us as existing ‘in itself,’ but only as existing iz the con- crete thing that is coloured, heavy, or extended. Yet in the things they do exist, and (in some cases at least) exist to the senses.
Colour only exists as the colour of something, li INTRODUCTION smell as the smell of something, shape as the shape of something, weight as the weight of something, size as the size of something; but the apple which has its own colour, smell, shape, weight and size, is not the apple of something, but the concrete apple itself, perceived as such by the senses. Colour, shape, and size are not ‘ things’; the apple is.
‘ Existences,’ then, are of various kinds, and if we take ‘ entity’ to mean the concretely existent that exists in itself and not in something else, then ‘ entities’ are a ‘kind’ or class of ‘ existences ’— those namely which are concrete and exist in them- selves—and ‘ qualities’ and ‘ quantities’ arc other kinds of existents, alike in that neither quality nor quantity can exist except in concrete entities.
‘ Entity,’ then, is a genus which may include other than material entities; for there may be (and Aristotle was profoundly convinced that there are) conscious beings that exist in themselves and have mental activities or attributes, but are wholly immaterial.
Material entities, then, may be a species of entities. But entitics themselves constitute a genus indeed (for theirs is one ‘ kind’ of existence, distinguishable from other kinds), but they form a supreme genus, and are not subject as a species to any higher genus or‘ kind.’ For ‘ existence ’ in the largest sense, the only term that can embrace entities and other kinds of existents, is not a ‘ kind’ at all, but embraces all that (in any sense of the word) ‘ is.’
This brings us to Aristotle’s celebrated and funda- mental doctrine of the ‘ Categories ’ or summa genera, each of which 15 a genus but not a species. We have here encountered three of them, entity, quality, liii INTRODUCTION quantity. There are more such categories, ‘ rela- tion ’ of one thing with another, for instance, actions and effects of actions, ‘place where’ and ‘ time when’ (ten in all); but it is entity, quality, and quantity, almost exclusively, that we are concerned with in the Physics, and we are concerned with them from the beginning to the end.
Once again, then, sense presents us with concrete stones, apples, trees, animals, each of which is per- ceived as an individual ‘ something ’ distinguishable from other ‘ things.’ Also there are substances or materials such as iron, clay, water, or air, which are distinguishable from each other, but can be divided into parts in a different way from that in which an apple can be divided; for if you divide an apple in half, it becomes two half apples, but not two apples, whereas if you divide a mass of iron in half, it becomes two masses of iron, each of which is just as much iron as the whole mass was, each existing initself. Again, when you divide an apple into two half apples, you divide one coloured thing into two coloured things, but neither the colour of the one nor the colour of the two exists ‘ in itself.’ The substance iron, then, is an entity, but colour is not.
From these things, organisms and substances, we must start. They ‘ exist’ in the primary sense, and we regard them as existing independently of our thought of them. When we think of them, we analyze them into the things they are and the qualities and so forth that they have, but we never perceive a thing apart from the qualities that it has, nor qualities apart from the thing that has them. The concrete or compositum, therefore, is the im- mediate datum of the senses. The distinction beliv INTRODUCTION liv INTRODUCTION tween the ‘ matter’ that constitutes the objectivity of all material things in common, and the special qualities that distinguish this thing from that, is purely mental, for these inferred ‘ components’ of the compositum are never met with apart except in the conceptual world of thought; and since these concepluals are distilled by the intelligence out of the perceived concretes, it follows that qualities and quantities, for example, cannot be thought of as existing unless the composita exist. The primacy of existence, then, belongs to the concrete.
Before leaving the Categories we may note that throughout the Physics Aristotle likes to begin his examination of any concept that presents difficulties or obscuritics, such as ‘ time,’ ‘ place,’ or ‘ movement,’ for example, by trying to determine to which of the categories it is to be referred, and whether it is a potentiality or an actuality. We are now prepared to understand the relevance of these inquiries.
4, Abstract thinking and Self-consciousness We shall be much concerned in the Physics with another set of abstractions—surface, point, distance or dimension, motion, for example—which cannot even be conceived as existing apart from bodies, but which can nevertheless be thought of (though not ‘imagined ’) apart from them and only so ‘ under- stood ’ (Mathematics and Physics).
This last set of concepts we shall naturally en- counter again as we come to Aristoile’s detailed treatment of them in the Physics, but we can already ly INTRODUCTION see how in Logic and Mathematics Aristotle con- ceived himself to have entered a conceptual or noétic world of abiding and changeless truths.« These sciences became to him the standards of pre- cision and certaintyin knowledge; andwe can discern through all his work a continuous effort to link his conclusions on to truths above them as well as building them up upon facts beneath them. But he is well aware that in this attempt we cannot always be equally successful and that we must be content in each case with such degree of precision and cer- tainty as that case allows. For instance, on the ground explored by Socrates, we note that every man recognizes a type of character and conduct (as distinct or at least differing from ability, for instance) that he admires and would like to see prevalent. We may ask what exactly the general characteristic is that distinguishes this type of human excellence from other kinds of human excellence, or excellence in general, as of an animal or a tool; and whal minor groups and distinctions are included in the main group (Ethics). Our conclusions in this field may be enlightening in a high degree, but they will * Unfortunately, we possess no works of Aristotle ex- ressly devoted to mathematical science, but his grasp of tundamental mathematical conceptions is apparent every- where, and it is clear that, next to logic, he regards mathe- matical science as presenting us with the highest type of generality and certainly of thought. Morcover, though mathematics 1s the most abstract of the special sciences, and so the remotest from materiality, it is the most uni- versally and most precisely applicable to material things, for its concepts inhere in them ἈΠ and so its inferences, while exceptionally rigorous on the conceptual side, are exception- aly capable of verification on the ‘sensible’ or practical side.
Wi INTRODUCTION hardly give us the ‘ parainount belief’ ¢ that Aristotle found, and the plain man stall finds, in Mathematics.
We will not follow Aristotle further in the vast survey covered by his extant works and indicated by the fragments and reports of those that are lost, but there is one all-important field which we cannot ignore.
In all these mental analyses and abstractions the mind itself is active, and the mind is conscious and can examine its own mentality. Neither the eye nor the visual sense can see or visualize its vision, nor can the hearing ear hear its hearing; but the thinking mind can think upon its thought. Sensa- tion is conscious, but mind alone is self-conscious. And so when we come to the human mind, of which the power of abstraction is a function, we have come to something more directly accessible to our con- sciousness than the material world itself, and we have here an announcement of reality more authentic and unchallengeable than that announcement of an objective world existing apart from our consciousness, which Aristotle and the plain man have allowed to pass unchallenged. Into this region too Aristotle carries us. Indeed we have been in it all along. Thought is a function of our vitality, and it was by thought that we distinguished, first, the inorganic from the organic or vital world, next, the unconscious life of plants from the conscious life of animals, and, lastly, the notes on the ascending scale of animal consciousness in sensation and in the traces left by sensation (recalling, image-making, and the rest) from 4 The phrase is Wordsworth’'s, not Aristotle’s. But the poet and the philosupher both express the same though? in reference to Mathematics, {ἵν INTRODUCTION each other and from the crowning self-conscious mentahty of man (Psychology).
It need hardly be pointed ont that in all these inquiries mental ‘defining’ (which is only to say ‘ distinguishing ἢ) must be perpetually aimed at, and that verbal ‘definitions’ will be of frequent use. Only by thcir aid can the concepts of the plain man be developed, clarified, and systematized for him.
It is by thinking, then, that we have arrived at the conception of thought itself as abstracted from all other vital functionings. But more than that, if we look back upon the processes involved in thinking, we find one that has been always present but of which we have had little direct occasion to speak. What is ‘inference,’ and when is it valid? Al thinking involves the belief that one thing ‘ follows upon’ another, or that, if two connected assertions are true, they warrant a third. To show that the conclusion really does follow is the office of the teacher; to ascertain it, of the discoverer; to make it appear to follow when it does not really do so is the trick of the sophist. To discover, therefore, the general and distinctive quality which gives an inference the right to demand our assent is a condi- tion sine qua non of fruitful thinking (Logic).
The results reached in this region of speculation, high up as they come in our progress from matter to mind, must in a systematic exposition come first of all, preceding even our examination of language; for it is of fundamental importance to distinguish between the éruth of an alleged inference and the validity of the inference. If we argue: ‘ Men are animals, and mammals are animals, therefore men are mamnials,’ ihe conclusion is true, but the litt INTRODUCTION ‘therefore’ false. Otherwise it would be equally true to say that because men are mammals and squirrels are mammals men are squirrels.
In studying the laws of inference we are studying the way m hich the mind works. But there is one more step to make. There is no point on which Aristotle is more insistent than that inference alone cannot furnish the mind. Everything cannot be proved by inference, for inference must start from something already accepted. The direct data of the senses are not inferred; they are known without inference. And in the mind itself there are truths which are not inferred or arrived at, but are directly known One of Aristotle’s favourite examples is that, as soon as we know what ‘ whole’ and ‘ part’ mean, we know that the whole is greater than the part. But the most fundamental of them all states that unqualified assertion and negation of the same thing cannot both be true. If‘ A is B’ and ‘A is not B’ are unqualified assertions, they cannot both be true. Axiomatic truths are truths that the human mind, by its very constitution, cannot do other than accept.
The constitution of the human mind, then, (1) gives it certain truths that it cannot deny or doubt, and (2) lays down certain paths of inference on which it can securely tread, and (3) gives it powers by which it can extract the permanent and universal out of the transient and the particular.
All certainty is based upon these certainties and can be no more certain than they. But Aristotle accepts them as absolutely valid. And these axiomatic certainties, together with the processes of our minds in dealing with them, we can ‘ under- stand.’ The data of our senses we must accept.
VOL. I lix INTRODUCTION But since self-consciousness in man devclops only under the stimulus of consciousness of an objective world other than itself, the impressions of the senses furnish all the material on which the mind can work till it rises upon matenal steps to the recognition of immaterial being—from the region of sensible facts to the region of intelligible truths.
And here, according to Aristotle, the study of Nature ends and the study that he sometimes calls Virst Philosophy and sometimes Theology begins.
5. Cosmogruphy and Theology In a connected series of works (the Physica, the De caelo, and the De generatione et corruptione *) Aristotle sets out, and attempts to justify, his theories as to the alternations and successions of physical phenomena which constitute the order of Nature.
He bases his theories on the data of the senses and the inferences that they appear to him to justify.
Among the most important of these inferences are; 1. That there cannot ever have been a time in the past when the order of Nature, as we know it, was not in actual operation; nor will there ever be a time when it ceases to operate.
2. That although the material universe and the processes of Nature must thus be regarded as ever- lasting, without beginning or end, yet they cannot be regarded as a self-contained and self-sustaining system, but point beyond themselves to an immaterial ® On the exclusion of the Afetcorologica from this list sce note on pp. Ixxv ἢ.
Ix INTRODUCTION order of existence, on which they depend for all their functionings.
The fist. of these conclusions explains why Aristotle, who is keenly interested in the origins and history of concrete human communitics and institu- tions, never atlempts to give us any kind of cosmo- gony, or account of the origin of cosmos, such as we find in the mythologies of all nations and, in some shape or another, in the speculations of many philosophers.
The second conclusion shows us how it is that Aristotle’s cosmography leads us to his theology, and even in a certain measure into it. This theology (Aristotle’s own term) is dealt with expressly in the work which Aristotle himself describes as ‘ Theology,’ or sometimes under the more comprehensive title of First Philosophy. This work is the treatise which we call the Metuphysics, because in the systematized Aristotelian canon it came ‘ after’ (meta) the group of physical treatises. But though theology is most expressly dealt with there, we have glimpses of it, not only in the De caelo, but also in the Physics, into which indeed it is inseparably mortised.
Many details of Aristotle’s cosmography will meet us in their places as we go through the Physics and will be dealt with as they arise. But it will be well to start with some general conception of the universe as it presented itself to his mind.
Aristotle’s universe, then, was a bounded plenum. That is to say, it was bounded by a nest of trans- parent spheres, which carried the stars and other heavenly bodies, all composed of the fifth or celestial element, within which the four-elemental world, with the earth at its centre, was contained. Through- Ἱχὶ INTRODUCTION out this whole universe, from the outmost sphere to the inmost core, there was no vacant space (or spaces) anywhere.: The sphericity of the earth herself was already firmly established m the science of Aristotle’s day, and this carried with 1 a recognition of the relativity of the conceptions of ‘up and down.’ To us ‘ up’ means in the direction from our feet to our heads, To the antipodes it means the direction from their feet to their heads—which coincides with our ‘ down.’ And every direclion between these opposites is someone’s ‘up’ and someone clse’s ‘ down.’ True to his general principle, Aristotle asks what is it in which all these opposites and variations agree, and he finds it in the fact that what ‘down’ means to everyone everywhere is ‘on a straight line from wherever they are to the centre of the carth.’ ‘Up’ means ‘ along the same line in the other direction’; and this definition holds everywhere in the universe.4 Heavy things have a trend towards the ceritre— « But the universe rotates on its axis, and movement anal of rotation or translation) presupposes direction.
ence the six elemental directions must be in some sense applicable to the universe es a whole. Now it is axiomatic with Aristotle that motion starts from the right. This is lustrated by the action of ἃ man hurling a stone or javelin or by our right-handed bowler in modern times. Motion begins by a swing forwurd of the right side counterclockwise. Therefore from right to left is the natural movement. And it is with the power eternally and without effort to move thus from mght to left that the eternal matter of the heavenly spheres 1s endowed, though with different degrees of intensity (apparently) according to the sphere or the place in the sphere which that particular matter occupies.
If I in this hemisphere regard myself as part of a solid sphere which is that of the fixed stars, and (ignoring for the lxil INTRODUCTION that is what being ‘ heavy’ means—and therefore the question why the mass of the heavy carth does not ‘ fall down through space’ is futile. ‘ Falling "ὦ means ‘moving towards the centre,’ and nothing else. ‘The earth is at the centre and has nowhere to fall to. It will be seen how very near Anistotle is to the modern conception of gravitation. If the mass of earth shapes itself as a sphere by mutual pressure, moment the secondary movements) take the sun as marking a particular place in that moving sphere, if I face the suniise and turn my body always to face the sun I should be moving with the movement of that sphere, and thal 1s from left to ryzht, which is clockwise. But that 1s cosmieally wrong. If, however, I were standing on my head or were standing up on my feet at the Antipodes, that same movement from Fast to West would have been from right to left or counter- clockwise, which is cosmically right.” Therefore the south pole is the top of the universe; the East is to the right and the West to the lefi. So in Lucan (Phars. iii, 248) the Arab troops of Pompey are spoken of as Umbras mirati nemorum non ire smistras —~wondering that, as they look on their own shadows, they did not find themselves moving counterclockwise, from right to left, as they had been used to in the southern hemisphere.
And contrariwise Dante on the mount of Purgatory having seen the sun rise and noting tts place some hours later 1s bewildered to find that it has moved from right to left counterclockwise, instead of fiom left to right clockwise as would be the case in the northern hemisphere (Purg. iv.
Plato too speaks of the East lying to the right when he is talking about the earth, but as lying to the left when he sup- poses the observer to be contemplating the heavens. (Lawes 760 Dp τὸ δ' ἐπὶ δεξιὰ γιγνέσθω τὸ πρὸς ἕω, Hpinomis 987 5 τρεῖς O° ἔτι φορὰς λέγωμεν ἐπὶ δεξιὰ πορευομένων μετὰ σελήνης τε καὶ ἠλίου.) So to this day in our modern maps the Fast lies to the right hand in the terrestial map and to the left in the celestial map.
See Book VIII, 264 b 17.
Ἱχ INTRODUCTION and if every several clod of earth, when separated from the mass, has a natural trend to join it, is not this the very formulating of the fact of masses gravitating to each other? No, for Aristotle ex- pressly tells us that a clod falls to the centre not because it is the centre of the earth but because it is the centre of the spherical vaull of heaven; and that, if the mass of earth were forcibly removed to the position of the moon and held there, a free clod would full not to it but to the centre of the universe. Thus he attributes to the ‘ centre’ a kind of active power of drawing heavy things (which are potentially subject to this power) towards itself; and unfortunately he attributes a corresponding active power to the inner celestial verge, by which it too attracts to itself the buoyant things which by potentiality are subject to its attraction.
Thus Aristotle commits himself to gravity and levity as two distinct qualities, both of them positive. Yire has levity alone, earth gravity alone; air and water have both levity and gravity in different degrees. This preconception prevents Aristotle from accepting the belief (already held by some other thinkers) that all the (non-celestial) elements have some gravity, though that which has least will rise above all the rest. Aristotle himself is constantly pushed in this direction by his own speculations, so much so as to be occasionally betrayed into in- consistencies with his own avowed theory, which nevertheless he vigorously and expressly defends.
The earth, with its swathings of water, air, and fire, Aristotle held to be, as a whole, stationary, as the central body of the universe, though its parts were (or were capable of being) in continuous change lxiv INTRODUCTION of relative position, by falling, rising, or crossing. This doctrine of the ‘ stationary earth’ (as we may call it for convenience) was not unchallenged in Aristotle’s day, and he himself was well aware that it anight be conceived either as ‘rolling’ or ‘ spin- ning, and he implies that, so fur as appearances go, a revolving earth under a stationary sky would not reveal itself as differing from a stationary earth under a revolving sky. But (in addition to less valid considerations) he made, as we shall sec, a truly scientific attempt to find an independent standard of reference by which to judge between the two hypotheses, and he decided in favour of the un- moving earth.