On the Infinite Universe and Worlds
(DE L'INFINITO UNIVERSO ET MONDI)
Albertino.  (a new speaker). I should like to know what is this phantasm, this unheard of monster, this human portent, this extraordinary brain, and what is the fresh news brought by him to the world? Or rather what are these ancient and obsolete views thus renewed, what these amputated roots sending forth fresh shoots in this our age?
Elpino. They are amputated roots which germinate, ancient things which return yet again, occult truths which are discovered; it is a new light which after the long night riseth over the horizon in the hemisphere of our knowledge and little by little approacheth the meridian of our intelligence.
Albertino. If I did not know my Elpino, I know what I should say.
Elpino. Say what you please. If you are as intelligent as I believe, you will agree with him as I agree. If you have greater talent, you will agree more rapidly and completely, as indeed I expect. Since those for whom the current philosophy and ordinary knowledge are hard, those who are disciples thereof but little adept (as is often the case though they know it not), such will not easily be converted to our view. For to them universal belief is most potent, and they are dazzled by the fame of those authors placed in their hands, so that they seek the reputation of expounders and commentators. But the others, by whom the received philosophy is clearly understood, have attained a point where they no longer propose to occupy the remainder of their days listening to others; they see by their own light, and with the activity of their mind's eye they penetrate every cranny; and Argus-like, with the eyes of their diverse knowledge they gaze through a thousand doorways on the aforesaid philosophy unveiled. Thus they will be able, on a nearer approach, to distinguish matters of belief accepted as truth on a distant view, by habit and by general consent, from that which truly is and must be accepted as certain, persistent in the very nature and substance of things. Truly, I say, they are ill able to accept our philosophy who have not the good fortune to be dowered with natural wit or are not at least tolerably familiar with diverse branches of knowledge; and especially they must have power of intellectual reflexion, whereby they can distinguish belief by faith from belief based on the evidence of true principles. For often an opinion is accepted as a principle that, if well considered, will be found to lead to an impossible conclusion, contrary to nature. I leave aside those sordid and mercenary minds that desire scarcely or not at all to attain truth, being content with what is generally estimated as knowledge, friends not of true wisdom but anxious only for the fame and reputation she bestoweth, seeking the appearance, not the reality [of knowledge]. For I say he is ill equipped for choice between diverse opinions and contradictory statements who is without sound and right judgement on these matters. He will decide with difficulty who hath no capacity to compare them, one with another, and he will experience great difficulty in comparing them when the differences that distinguish them are beyond his understanding. Right hard it is to understand wherein they differ, since the substance and being of each is hidden. And this can never be evident except through a clear understanding of the reasons and principles on which each is based. After you have looked with the mind's eye and considered with well-controlled perception the foundations, principles and reasons on which are based these diverse and opposed philosophies, after you have examined the nature, the substance and the peculiarity of each and weighed one against another on the scales of the intellect, distinguished their differences and compared and judged straightly between them, then without hesitation you will readily choose to consent to the truth.
Albertino. Aristotle, our prince of philosophers, affirmeth that it were vain and foolish to exercise ourselves to oppose vain and foolish opinions.
Elpino. Well said. But if you examine the matter, this advice and counsel applieth against his own opinions when they are clearly foolish and vain. He who would judge correctly must as I have said be able to renounce the habit of belief. He must regard two opposed views as equally possible and must dismiss all prejudice imbibed since his birth -- both that which we encounter in general conversation, and that by which we are (though as dying to the crowd of men) reborn through philosophy among those scholars who are esteemed wise by the majority of men at a certain period. When controversy ariseth between different persons regarded as wise among different peoples and in different ages, I would say that if we would judge aright, we must recall to mind the warning of this same Aristotle that, through concentrating regard upon few facts we may sometimes [too] readily deliver ourselves of opinions; and sometimes an opinion doth command our assent merely by force of custom, whereby that appeareth to us necessary which in fact is impossible; or we perceive and learn that to be impossible which is most true and necessary. And if this occurreth in manifest matters, what must happen in those which are doubtful and depend on well-grounded principles and solid foundations?
Albertino. It is the opinion of the commentator Averroes and of many others that what Aristotle hath not known cannot be learned.
Elpino. Both he and the multitude of his followers had so low a talent and were in such deep darkness that they could see nothing higher and more brilliant than Aristotle. Wherefore if he and others when they allow themselves to let fall such opinions were to speak with strict accuracy, they would say that Aristotle appeareth to them as a God; thereby they would not so much exalt Aristotle as manifest their own worthlessness. For to them the matter appeareth even as to the ape her own children appear the most beautiful creatures in the world, and her own ape husband the fairest of mates.
Albertino. "The mountains do bring forth." 
Elpino. You will see that it is no mouse to which they give birth.
Albertino. Many have crossed weapons with Aristotle; but their castles have fallen, their shafts are blunted, their bows have broken.
Elpino. What happeneth when one vain thing maketh war with another? One is all-victorious but doth not thereby cease to be vain; and will he not finally be discovered and vanquished by truth?
Albertino. I maintain that it is impossible to demonstrate that Aristotle is in error.
Elpino. That is too rash a statement.
Albertino. I say it only after having examined well and considered yet further that which Aristotle saith. And so far from having detected in him any error, I can discern naught of divinity that he doth not know: and I must believe that no other man can perceive that which is invisible to me.
Elpino. You measure then the stomach and brain of others by your own, and believe that to be impossible to others which cannot be achieved by yourself. There are in this world those, so unlucky and unhappy that not only are they deprived of every good, but they have been fated to receive as eternal companion that Erinnys and infernal Fury which forceth them voluntarily to cloak their eyes with a black veil of corrosive jealousy, that they may not perceive their own nakedness, poverty and misery, nor the ornaments, riches and delights of others. They prefer to pine away in filth and proud penury and to remain buried under a dung heap of obstinate ignorance rather than to be discovered turning to a new discipline or seeming to confess that hitherto they had been ignorant, and had been guided by an ignorant man.
Albertino. Would you then for example prefer that I should become a disciple of this fellow? What, I who am a doctor, approved by a thousand academies, I who have publicly professed philosophy in the first academies of the world, am I now to deny Aristotle, and crave to be taught philosophy by such fellows [as Theophilo]?
Elpino. For my part, I would be taught not as a doctor but as an unlearned man; not in the character that I should, but on account of that which I do not fulfil, I would learn. I would accept as master not only this man, but any others whom the gods have ordained to that office, for they enable me to understand that which I do not now understand.
Albertino. Then you would make me a child again?
Elpino. Rather that you should discard childishness.
Albertino. I give you thanks for your courtesy, that you would so advance and exalt me as to permit me to enter the audience of this miserable wanderer. All know how he is hated in the academies, how he is the adversary of every accepted doctrine, praised by few, approved by none, pursued by all.
Elpino. Yea, he is persecuted by all, but by what sort of people? He is praised by few, but those the best and heroes. Adversary of accepted doctrine not as doctrine or as accepted, but because it is false. Hated by the academies because where there is contrast there is no love; distressed because the multitude is opposed to him who separateth himself from them, and he who placeth himself on high maketh himself the target to many. To describe to you his mind as regards speculative matters, I will tell you that he is not so desirous to teach as to understand; he will take it as better news and will be better pleased when he knoweth that you wish to teach him (in so much as he may hope for some result) than if you were to tell him that you wish to be taught by him, for his desire is rather to learn than to teach, and he regardeth himself as apt rather to the former than to the latter. But here he cometh with Fracastoro.
Albertino. You are most welcome, Philotheo.
Philotheo. And you no less so.
Albertino. "If in the forest I chew straw with the ox, the sheep, the goat, the ass and the horse, then, to improve my livelihood, without sin do I come hither to make myself a disciple." 
Fracastoro. Welcome indeed.
Albertino. I have up to now esteemed your views unworthy to be heard, still less to be answered.
Philotheo. In my early youth and up to a certain term I judged similarly, being entirely occupied with Aristotle.  Now that I have seen and meditated more and have a mature experience, I should be able to judge matters: it may be that I have become foolish and have lost my wits. Since this is a sickness which no one perceiveth less than the patient himself, I am the more readily exercised by a suspicion that I have moved from learning to ignorance, and I am therefore most happy to have come across a physician esteemed by all as able to release me from such a mania.
Albertino. Nor Nature nor I can aught do, if the disease hath penetrated through to the bone. 
Fracastoro. Prithee, Sir, feel first his pulse and examine his urine; for afterwards, if we cannot effect a cure, we shall be wary of him.
Albertino. The method of feeling the pulse is to see whether you can resolve and find escape from certain arguments which I will now recite to you, which conclusively demonstrate that a plurality of worlds is impossible and an infinity of worlds even less possible.
Philotheo. I shall be in no small degree indebted to you when you have taught me this. And should your intention come not to effect, I shall be indebted to you for confirming me in my own opinion. For indeed I deem that from you I shall perceive the full force of the contrary argument; and since you are most expert in the received sciences, you will easily perceive the strength of the foundation and the structure thereof by their differences from our principles. That there may be no interruption in the argument, and that each may have fair opportunity to explain his own views, will it please you to bring forward those arguments which you consider most solid and important and which appear to you most conclusive?
Albertino. I will do so. First then, that beyond this world  there is believed to be neither time nor space, for there is postulated one primal heaven, a body most distant from us -- the primum mobile; wherefore we are accustomed to name heaven that which is on the utmost horizon of the world; on it are all the still and motionless, fixed and still bodies which are the intelligences endowing the orbs with motion.  The world again is divided into a celestial and an elementary body, the latter being bounded and contained, the former the containing limit. And the world  is so ordered in rising [scale] from the densest to the most subtile which is above the convex of fire. On this are fixed the sun, moon and other stars, and it doth constitute a fifth essence. The quality thereof is such that it strayeth not forth into the infinite, for it could not be joined to the primum mobile; and it encountereth not the other elements, for these would then be around it; and the incorruptible and divine would be contained and comprised by corruptible bodies, which is not seemly. For to the divine there appertaineth a nature conditioned to Form and Action, and therefore to the function of containing, and endowing others with definite form and limit, being itself without limit, form or substance. Having argued thus, we proceed with Aristotle to maintain that  if there be a body beyond this heaven, it must be either a simple or a compound body. And however thou mayest reply, I ask thee further, will the body occupy a position impelled by his inner nature, or by the accident of position and by outward constraint? We will shew that no simple body can be there, for it is impossible for a perfect sphere to change position. Since the centre thereof is immutable, the position cannot change, for only by constraint can it attain to any but his own proper position; and a sphere can suffer no constraint, active or passive. Similarly it is impossible that there be outside the heaven a simple body that moveth in a straight line; whether it be heavy or light, it cannot naturally be there, since the natural positions of simple bodies are not those which are called beyond the world: nor can you say that these bodies are there by accident [or constraint by other bodies], for in that case other bodies would be there of their own nature. It is then proved that there are no simple bodies besides those which make up our own world, and these bodies are endowed with three kinds of local motion. Consequently there can exist beyond the world no other simple body, and therefore also no compound body, since the latter is compound of the single, and becometh again resolved thereto. It is thus manifest that there exist not many worlds, for the heaven is unique, perfect and complete, and there is and can be no other like it. Wherefore it may be inferred  that outside our world  there can be neither Space, Plenum, Void nor Time. Space is not there, for if it be a plenum, it will contain either a simple or a compound body; and we have shewn that beyond the heaven is neither simple nor compound body. But if such space be void, then, according to the nature of a void, which is defined as space capable of containing body, a body may reside therein; and we have shewn that beyond the heaven no body can exist. And Time is not there, because Time is the number of Motion, and Motion can only be postulated of body; thus where there is no body, there is no motion and therefore no measurement of motion, and without this there is no Time. Moreover, since we have proved that there existeth no body beyond the world, therefore we have demonstrated that neither Motion nor Time is there, nor aught temporal nor endowed with motion. Wherefore there is but one world.
Secondly,  the uniqueness of the world may be inferred from the unique motive body [the primum mobile]. It is agreed that circular motion is truly unique, uniform, without beginning and without end. If it be unique, it is an effect which can result from only one cause; if then there is one primal heaven beneath which are all the lower heavens, and these conspire to make up a single order, then there can be but one governing and motor power. This being incorporeal, cannot be multiplied by addition of matter. If the motive power is unique, and if a single motive power can give rise only to one motion, and motion whether complex or simple can take place only within a simple or compound mobile body, it followeth that the mobile world  is one, wherefore there can be no other worlds.
Thirdly,  a unique world may be inferred from the positions occupied by bodies in motion. There are three kinds of moving bodies, those generally heavy, those generally light, and that which is neither. [To the first kind belong] earth and water; [to the second] air and fire; [to the third] the heaven. Similarly there are three different fields for moving bodies. The lowest and central, occupied by a very heavy body; the uppermost region, furthest from this, and the midway region, between the central and the uppermost. Thus the first is heavy and belongeth to the centre; the second neither heavy nor light, belongeth to the outer circumference, while the third is light and belongeth to the space between the other two. There is therefore a lowest region to which tend all heavy objects from any world, and there is an upper region to which tend all light objects from any world; hence there is a region in which the heaven, to whatever world it may belong, doth travel. If then there is but one space, there is also but one world, not many.
Fourthly,  I declare that [if there were more than one world] there would be various centres toward which move the heavy objects of diverse worlds, and there would be several horizons toward which light objects would move. These positions in diverse worlds differ not in kind but only in number. Thus the centre will be further distant from another centre than from his own horizon. But one centre and another are alike in kind, while centre and horizon are of opposed nature. Wherefore the distance through space will be greater between those of similar kind than between those that are opposed. This is contrary to the nature of such opposites: for when it is said that contrary elements are furthest removed from one another, this should be understood to refer to distance in the same space, which must indeed be between contrary sensible bodies. You see then what would follow from supposing more than one world. It is clear that such a hypothesis is not only false but impossible.
Fifthly,  if there be more worlds of the same kind, they must be equal, or certainly proportional in size  which cometh to the same thing as regardeth our proposition. If this be the case, there cannot be more than six worlds adjoining our own: for not more than six spheres can touch a single one without their penetration, just as not more than six equal circles can touch one another without the lines intersecting [Diagram VII]. If this be so, several [i.e., six] horizons will be ranged -- at the respective points where the six worlds touch our own world or another -- around a single centre. But since the virtue of two opposed elements should be of equal power, and since inequality followeth from this arrangement, you will make the upper elements more potent than the lower, you will make the former victorious over the latter and thus you will dissolve this body.
Sixthly, since if the circular surfaces of the diverse worlds touch only at a point, there must necessarily remain a certain space between the convex circumference of one sphere and that of another, and either there is something within this space which filleth it, or there is nothing [Diagram VII]; if there is something, it certainly cannot be of the nature of an element, distant from the convex surface of a sphere, because, as is evident, such a space must be triangular and enclosed within three arcs that form part of the circumferential surface of three worlds: and thus the centre [of a triangle] will be found to be rather distant from the parts nearest to the angles but most distant from the spheres,  as may clearly be seen. It will then be necessary to imagine new elements and a new world filling that space, different from our elements and our world. Otherwise it is necessary to suppose a vacuum in the triangular space, and this we postulate to be impossible.
Seventhly, if there are other worlds, they must be either finite or infinite. If they are infinite, the infinite will have issued in determined action.  This is for many reasons deemed impossible. But if they are finite, they must be a definite number. And then we shall ask ourselves, why are there exactly so many and neither more nor less? Why is there not one more? What would happen if there were this or that additional world? Whether they be even or uneven in number, why should they be in this rather than in that category? And indeed why is all this matter divided into many worlds instead of being agglomerated in a single globe? Since unity is better than multiplicity, ceteris paribus, why is the substance divided among four or six or let us say ten earths, rather than forming a single great and perfect globe? Indeed, just as there ariseth from the possible and the impossible a finite sooner than an infinite number; so, as between the convenient and the inconvenient, unity is more rational and natural than multiplicity or plurality.
Seventhly [sic],  we see nature in all things close herself in the smallest compass, for as she lacketh not things necessary, so she aboundeth not in superfluities. Since then she can produce her whole effect with those works that are in this world, it were not reasonable to wish to feign that there be more worlds.
Eighthly,  if there were an infinity of worlds or even more than one, this would be the case chiefly because God could fashion them thus, or rather because they could depend on God. But most true though this may be, it doth not follow that these worlds exist, for besides the active power of God there is needed the passive power of things. For that which can be created in nature dependeth not upon the absolute divine power, since not every active power transformeth itself into passive, but only that which hath subject proportionate to itself; that is, a subject able to receive the efficient act in its completeness. Now naught affected hath such correspondence with Prime Cause. In so far then as concerneth the nature of the world, there cannot be more than one, even though God can make more.
Ninthly,  the plurality of worlds is outside all reason, for there would be in them no civil virtue, which consisteth in civil intercourse. And the gods who had created diverse worlds would have done ill, in that they had not contrived that the citizens thereof should have commerce one with another.
Tenthly,  the plurality of worlds would place obstacles to the labour of every motive force or divinity. For since the spheres must touch one another at certain points [Diagram VII], the one would hinder the movement of the other and the gods could hardly govern the world through motion.
Eleventhly, a plurality of individuals cannot arise from a single one, unless by nature's process of multiplication by division of the substance, which is none other than generation. For it is said by Aristotle and by all Peripatetics that individuals of a single kind multiply only by the act of generation. But those who maintain the existence of a plurality of worlds, of the same matter and kind of form, do not assert that one is transformed into another, or is generated from another.
Twelfthly,  to perfection nothing can be added. If then this world is perfect, certainly there is no need for another to be added to it. The world is perfect, firstly as a kind of continuum which is not bounded by another kind of continuum. For an indivisible mathematical point culminateth mathematically in a line which is a kind of continuum; the line culminateth in a surface which is a second kind of continuum; the surface in a solid body which is the third kind of continuum. A body migrateth not, nor removeth into another kind of continuum. But if it be part of the universe,  it is bounded by another body; while if it is itself the universe,  it is perfect and is bounded only by itself. Thus the world or universe  is unique, and should be perfect. These are the twelve [thirteen] arguments which I desire for the moment to put before you. If you satisfy me concerning these, then I am completely satisfied.
Philotheo. But, my Albertino, he who proposeth to defend a proposition must first (unless he be indeed a fool) have examined the contrary arguments, just as a soldier would be foolish if he undertook to defend a castle without having considered the circumstances and places from which it may be assailed. The arguments brought forward by you, if indeed they be reasonable, are well known and oft repeated. Most effectual reply may be made to them all by a mere consideration on the one hand of their basis, and on the other of the measure of our own assertion. I will make both clear to you by the course of my reply, which shall be brief. For if you need further speech and explanation, I will leave you to the care of Elpino who shall repeat that which he hath heard from me.
Albertino. First, I pray you, make me perceive that this method will not be fruitless nor devoid of satisfaction to one who desireth knowledge, and that I shall certainly not be weary listening first to you and then to him.
Philotheo. To the wise and judicious, among whom I count you, it sufficeth to demonstrate in what direction consideration must be given. For they themselves will then proceed deeper in appraising the means by which one or other contrary opinion may be reached. As to your first doubt, we will say that your whole framework crumbleth, since there exist not these differences between various orbs and heavens, and the stars through this vast ethereal space move of their own nature, each spinning around her own centre and also revolving around another centre. There is, in fact, no primum mobile that draweth those many bodies around ourselves as centre. Rather it is our globe which causeth the appearance of this happening, for reasons which Elpino will expound to you.
Albertino. Willingly I will hear him.
Philotheo. When you have heard and have well marked that such an opinion is contrary to nature, while ours is consonant with all reason, perception and verification in nature, you will no longer say that there is an edge or limit either to the extent or to the motion of the universe; you will esteem the belief in a primum mobile, an uppermost and all-containing heaven, to be a vain fantasy. You will conceive rather a general womb in which are situate all worlds alike, even as this terrestrial globe in this our local space is surrounded by our atmosphere and is in no way nailed or attached to any other body, nor hath any base but his own centre. And if it is found that this our globe cannot be proved to be of a constitution different from the surrounding stars, since it manifesteth accidents no different from theirs, then should it no more than any one of them be regarded as occupying the central position of the universe, nor as being more fixed than they, nor will they appear to revolve around it rather than it around them. Whence, since such indifference on the part of nature must be inferred, so also we must infer the vanity of [imagined] deferent orbs; and we must accept the inner impulse toward motion implanted in the souls of these globes, the indifference throughout the vast space of the universe and the irrationality of conceiving any edge or external shape thereto.
Albertino. These are things, indeed, which are not repugnant to nature and may be more convenient, but they are hard to prove; and great talent is needed to find an escape from the contrary appearance and arguments.
Philotheo. Once the end of the thread is found, the tangle is easily unravelled. For the difficulty proceedeth from the method and from an unfitting hypothesis, namely, the weight and immobility of the earth, the position of the primum mobile with the other seven, eight, nine or more [spheres] on which are implanted, impressed, plastered, nailed, knotted, glued, sculptured or painted the stars -- and that these reside not in the same space as our own star, named by us earth. But you shall hear that her space, shape and nature are neither more nor less elementary than those of the other stars, nor is she of a nature less apt to motion than each of those other divine living creatures.
Albertino. Truly if this thought is once harboured in my mind, all the others proposed by you will in turn easily be accepted. You will have at once cut the roots of one philosophy and implanted those of another.
Philotheo. Likewise you will with good reason scorn to accept any longer common opinion based on the impressions of the senses  that there existeth a highest horizon, most lofty and noble, the frontier of the divine motionless substances which are the motive powers of these finite orbs. And you will admit that it is at least equally credible that just as this earth is an animal, mobile and travelling by virtue of her own inner nature, such too are all those others. You will regard as mere fantasy, incapable of demonstration, the view that these bodies derive their motion from the motion and transporting power of a body which is without tenacity or resistance, more rare and subtle than the air we breathe; whereas you will consider that our view conformeth to every sane sense-perception and to every well-founded reasoning. You will declare to be no nearer to truth the notion of spheres with concave and convex surfaces moved round and drawing with them the stars; but you will receive as true and in harmony with our intellect and with natural convenience the belief that the stars in conformity with their own inner nature and life follow -- as you shall presently hear -- their circular courses around and toward one another, without fear either of sinking downward or rising upward; since in the immensity of space there is no distinction of upper, lower, right-hand, left-hand, forward or backward. You will see that beyond the imagined circumference of the heaven, there can be either a simple or a composite body moving in a straight line; for just as the parts of our own globe move in a straight line, so also and no less easily, may the parts of other bodies. For our own globe is composed of no different material to those beyond, nor doth ours appear to revolve around them any less than they around us.
Albertino. I perceive then more clearly than ever that the smallest error at the start may cause the greatest difference and peril of errors at the finish.  A single simple inconvenience will multiply little by little, and ramify into an infinity of others -- even as from a little root may grow a vast plant with innumerable branches. On my life, Philotheo, I do greatly desire that thou mayest prove to me this which thou proposest; and since I regard it as worthy and probable, that thou mayest make clear to me also the truth thereof.
Philotheo. I will do all for which time and occasion may serve, submitting to your judgement many things which have been hidden from you heretofore not through incapacity but through inadvertence.
Albertino. Put the whole before me, in form of article and conclusion, for I know that before you accepted your present opinion you have been able to examine carefully all which pointed to contrary conclusions; for I am sure that the secrets of the accepted philosophy are as clear to you as to myself, wherefore pray proceed.
Philotheo. It is then unnecessary to investigate whether there be beyond the heaven Space, Void or Time. For there is a single general space, a single vast immensity which we may freely call Void; in it are innumerable (innumerabili et infiniti) globes like this one on which we live and grow. This space we declare to be infinite, since neither reason, convenience, possibility, sense-perception or nature assign to it a limit. In it are an infinity of worlds (infiniti mondi) similar to our own, and of the same kind. For there is no reason nor defect of nature's gifts, I mean either of active or of passive power, that preventeth their existence in all the rest of space, which is identical in natural character with our own, just as they exist in the space around us.
Albertino. If that which you first said is true (and so far it appeareth no less likely than the contrary view), then this which you now affirm must necessarily follow.
Philotheo. Beyond the imagined convex circumference of the world is Time. For there is the measurement and true nature of motion, since similar moving bodies are there. Let this be partly accepted, partly proposed in regard to what you have already advanced as the First argument for a single world. As for your Second argument, I declare to you that there is in truth one prime and principal motive power; but not prime and principal in the sense that there is a second, a third and other motive powers descending down a certain scale to the midmost and last, since such motive powers neither do nor can exist. For where there is infinite number, there can be neither rank nor numerical order, although there is rank and order according to the nature and worth either of diverse species and kinds, or of diverse grades of the same kind and species. There are then an infinity of motive powers  as there are an infinity of souls inhabiting the infinite spheres; and because these are form and natural action,  there is in relation to all of them a sovereign on whom all depend, a first principle who endoweth with the capacity of motion spirits, souls, gods, heavenly powers and motive forces; and he setteth in motion matter, body, animated being, lower orders of nature, and all which may move. There are then [repeats Philotheo] an infinity of mobile bodies and motive forces, and all of these reduce to a single passive principle and a single active principle, just as every number reduceth to unity, and as infinite number doth coincide with unity; and just as the supreme Agent and supreme active power doth coincide in a single principle with the supreme potentiality, patient of all creation, as hath been shewn at the end of our book On Cause, Origin and the One. In number then, and in multitude, there is infinite possibility of motion and infinite motion. But in unity and singularity is infinite motionless motive force, an infinite motionless universe. And the infinite number and magnitude coincide with the infinite unity and simplicity in a single utterly simple and indivisible principle, which is Truth and Being.  Thus there is no primum mobile, no order from it of second and other mobile bodies either to a last body or yet to infinity. But all mobile bodies are equally near to and equally far from the prime and universal motive power, just as (logically speaking) all species are equally related to the same kindred, and all individuals to a single species. Thus from a single infinite and universal motive force in a single infinite space there is but one infinite universal motion on which depend an infinity of mobile bodies and of motor forces, each of which is finite both as to size and power. As for the Third argument, I declare that there existeth in ethereal space no determined point toward which heavy objects move as to a centre, and from which light bodies separate themselves as seeking a circumference; for there is in the universe neither centre nor circumference, but, if you will, the whole is central, and every point also may be regarded as part of a circumference in respect to some other central point. As for ourselves, that object is called by us heavy which moveth from the circumference toward the centre of our own globe; and that object is called light which moveth in the opposite direction toward an opposite goal; and we shall see that nothing is heavy which is not also light. For every part of the earth in turn changeth both site, position and also composition, so that through the long course of centuries no central particle faileth to reach the circumference, and no particle on the circumference faileth to become central or to tend toward the centre. We shall see that weight and lightness are no more than the impulse of particles of a body to their own natural containing region, wherever it may be, in which they are best conserved. Wherefore there are no differences of position attracting or repelling different parts. But the desire for self-preservation is an inner force that impelleth every object -- provided no obstacle intervene -- to flee as far as possible from contrary matter and to join with a convenient neighbour. Thus then, the particles from the circumference of the moon and of other worlds similar to our own in species or kind seek to unite in the centre of their own globe as though impelled by their own weight; while subtilized particles, as though impelled by their own lightness, disport themselves toward the circumference. And this is not because the particles either flee from the circumference or attach themselves to it, for if this were the case, the nearer they approached thereto, the more rapid would be their motion, and the further they retired from it the more forceful would be their advance to a new position; whereas we observe just the contrary, that if they are impelled beyond the terrestrial region, they will remain poised in the air, and will neither mount on high nor sink downward until, either acquiring greater weight by apposition of parts or by increased density through cold, whereby they traverse the air below them and return to their own containing body, or else becoming rarefied and dissolved by heat, they are dispersed into atoms.
Albertino. Oh how my mind will be at rest when you have more fully shewn me that the stars are [of a nature] indistinguishable from that of this earthly sphere.
Philotheo. Elpino will easily repeat this to you as he hath heard it from me; and he will make you realize more distinctly that no object is heavy or light in respect to the universe, but only in respect to his own region and the body which containeth or maintaineth him. For the tendency to maintain an existing condition impelleth every change of position, as when seas and even drops of water assemble together, or again disperse as happeneth to all liquids exposed to the sun or to other fires. For all natural motion, impelled by the inner principle of a body, is naught but an attempt either to escape an inconvenient and contrary body or to follow a friendly and convenient body. Wherefore nothing changeth position unless driven forth by his contrary; nothing in his natural position is either heavy or light; but the earthy matter, raised up into the air while seeking her natural position, is heavy and is felt to be heavy, just as water if suspended in the air is heavy, though in her own region water is not heavy. Thus to those who are submerged, the whole of the water is by no means heavy, whereas a little vase full of water will become heavy if situated above the air beyond the dry surface. The head on his own body is not heavy; but the head of another laid on top will be heavy, the reason being that the latter is not in his natural position. If then weight and lightness are merely an impulse to a position of safety and escape from a contrary position, it followeth that nothing is by nature either heavy or light, and that nothing is endowed either with weight or lightness if so far distant from his preserving [environment] or so far removed from his contrary as not to be affected by the helpfulness of the one or by the harmfulness of the other. But if, becoming aware of a harmful environment, it groweth desperate and is perplexed and irresolute, it will be vanquished by its contrary.
Albertino. Thou hast promised and in great part thou hast performed wondrous things.
Philotheo. To avoid repetition a second time, I now commit you to Elpino who will narrate to you the remainder. 
Albertino. It appeareth to me that I understand all. One doubt raiseth another and one truth demonstrateth another. I begin to understand more than I can explain, and I begin to doubt many things which heretofore I have held as certain. Thus I feel myself little by little prepared to agree with you.
Philotheo. When you have heard me in full, you will give me your full assent. For the moment, bear this in mind, or at least be not now as resolutely in favour of the contrary opinion as formerly you shewed yourself before you entered into the controversy. For little by little, as occasion serveth, we shall reach a complete exposition of the subject -- which dependeth indeed on several principles and reasonings. For as one error leadeth to another, so is one discovered truth followed by another.
Concerning your Fourth argument, we declare that albeit there are as many centres as there are individual globes, spheres or worlds, yet it doth not follow that the particles of each are related to any centre but their own, nor that they depart to any circumference but that of their own region. Just as the particles of our earth do not seek any centre but their own, nor do they strive to unite with any but their own globe, so also the humours and parts of an animal ebb and flow in their own subject, nor do they appertain to some other body of a different number. As to your reasoning of the inconvenience that a centre would become further removed from another centre than from the circumference of his own globe, though centres are of the same species while the centre and circumference are of contrary nature and should therefore be furthest removed from one another, I reply as follows: Firstly, that contraries need not be at the furthest distance one from another, inasmuch as one may influence the other or may be patient of influence therefrom; as we see that the sun is disposed very close to us among the earths which encircle it, since the order of nature causeth an object to subsist, live and derive nourishment from his contrary, as the other becometh affected, altered, vanquished and transformed by the first. Moreover a short while back we discussed with Elpino the disposition of the four elements which all contribute particles in the composition of each globe, one particle being placed within another, one mixed with another. Nor are they distinguished as a containing and a contained body respectively. For where there is dry earth, there also are water, air and fire, either patent or latent. The distinction made by us among the globes, that some, like the sun, are fiery whilst others, as the moon and the earth, are watery, doth not depend on these bodies consisting solely of a single element, but merely on the predominance of a single element in the mixed substance. Furthermore it is a most false belief that contraries are situated furthest from one another. For in all objects the elements become naturally combined and mixed. And the whole universe, both in the principal and secondary parts, consisteth solely of such conjunction and union, since there is no portion of the earth which is not intimately mixed with water, without which it would have neither density, connection of the atoms withal nor solidity. Moreover what terrestrial body is so dense that it lacketh insensible pores? Without them such bodies would no longer be divisible nor penetrable by fire nor by the heat thereof which is, however, sensibly perceived to issue from the substance of these bodies. Where then in this thy body is a cold and dry portion which is not joined to a moist and warm part, no less appertaining to thy body? This distinction of elements resteth then not on nature but on logic. And if the sun be in a region far removed from that of our earth, yet neither air nor dry land nor water is further from him than from our own globe. For the sun, like our earth, is a composite body, though in him there predominateth a certain one of the above-mentioned four elements, and in our earth, another. Moreover if we would have nature conform to that logic which would impose the greatest distance between contrary bodies, then, between thy fire, which is light, and the heavy earth must be interposed thy heaven, which is neither heavy nor light. Or if indeed thou wouldst limit thy statement by saying that this order is to be understood only of those that are called the four elements,  nevertheless thou wouldst be forced to arrange them in different order: I mean that water must then occupy the central position of the heaviest element, if fire is on the circumference of the elemental region in the position of the lightest element; for water which is cold and moist is in both these qualities opposed to fire and must therefore be at the greatest distance from the hot  and dry element; while air which you declare to be hot and moist should be furthest from the cold and dry earth. You see then how this Peripatetic proposition remaineth unstable whether examined according to the objective truth of nature or according to his own logical principles and foundations. 
Albertino. I see it most clearly.
Philotheo. You see further that our philosophy is by no means opposed to reason. It reduceth everything to a single origin and relateth everything to a single end, and maketh contraries to coincide, so that there is one primal foundation both of origin and of end. From this coincidence of contraries we deduce that ultimately it is divinely right to say and to hold that contraries are within contraries, wherefore it is not difficult to compass the knowledge that each thing is within every other -- which Aristotle and the other Sophists could not comprehend.
Albertino. Most willingly I hear you. I know that so many matters and such diverse conclusions cannot be proved all at once, on a single occasion. But since you have revealed to me the inconvenience of those beliefs that I once deemed necessary, I become doubtful of all others which for the same or similar reasons I would deem necessary. Therefore I prepare myself to listen with silent attention to the foundations [of your philosophy], your principles and your reasons.
Elpino. You will see that Aristotle brought no golden age to philosophy. For the moment, those doubts put forward by you are dispelled.
Albertino.  I am not so curious concerning those, for I am most anxious to hear the doctrine concerning principles by which these and other doubts will be resolved by your philosophy.
Philotheo. These we will consider presently. As for your Fifth argument, you should know that if we conceive many and an infinity of worlds of nature and composition such as you are accustomed to imagine, it would be almost as though, besides a spherical world containing the four elements ranged in the usual order, and the eight, nine or ten other heavens of a different substance and nature encircling these and revolving rapidly around them, we should then imagine innumerable other worlds also spherical and endowed with motion like our own. Now we should need to produce arguments, and invent how one of these worlds could touch or be continuous with the rest; now we should proceed with fantastic imagination to discuss in how many points the circumference of one world may touch those of the surrounding worlds. You would then see that however numerous were the horizons around a world, they would belong not to one world, but would have each one the same relation to his own centre. For they exercise their influence where they revolve and at the centre around which they spin, just as, if a number of animals were confined together, touching one another, it would not follow that the limbs of one could belong to the limbs of another in such a manner that one or each of them could possess several heads or bodies. But we, thanks to the gods, are free of the embarrassment of craving such explanations. For instead of these numerous heavens, these many swift and stubborn mobile bodies, straight and oblique, to the east and to the west, on the axis of the world, on the axis of the zodiac, in so far and so much, in greater or lesser declination, we have but one single heaven, a single space through which our own star in which we reside, and all other stars perform each their own circuits and courses; these are the infinite worlds, the innumerable stars; this is the infinite space, the heaven comprehending all, traversed by all. Banished is the fantasy that the whole revolveth around ourselves as centre; for we are now well aware that it is our earth which revolveth; and that she, spinning around her own centre, hasteneth during each twenty-four hours to the successive view of the surrounding luminaries. Therefore also the notion is banished of deferent orbs on which the stars are fixed, encircling our own space. To each star we attribute only his own motion, named epicycle, differing from that of each of the other mobile bodies. These orbs, impelled by no other motive force than the spontaneous impulse of the spirit within each, follow, just as doth our own earth, each his course around his own centre and around the fiery element, during long centuries if not indeed to eternity. Here then is the true nature of the worlds and of the heaven. The heaven is such as we see it around our own globe which is, like the other globes, a luminous and excellent star. The worlds are those whose brilliant shining surfaces are distinctly visible to us, and they are placed at certain intervals one from another. But nowhere is one of them nearer to the other than the moon may be to our earth, or our planets to our sun; so that those of contrary nature do not destroy but rather nourish each other, and those of similar nature do not impede but rather give space to each other. Thus from one to another cause, little by little, from season to season, our most frigid globe is heated by the sun, now from this side, now from that, now on this part of her surface, now on that; and through certain vicissitudes she now yieldeth and anon claimeth place from the neighbouring earth which we name the moon, so that now one, now the other body is respectively further from or nearer to the sun: wherefore the moon is named by Timaeus and other Pythagoreans the counter-earth.  These then are the worlds inhabited and cultivated each by their own living beings,  and themselves the principle and most divine of all living beings  in the universe; and each is composed of four elements no less than is this earth on which we find ourselves, though in some there may predominate one active quality, in others, another; so that these are perceptible to us by means of the waters thereof, those by their fire. Besides the four elements that compose the heavenly bodies, there is as we have said a vast ethereal region in which they all move, live and grow, the ether which both envelopeth and penetrateth all things. In so far as it entereth into and formeth part of the mixture of the elements, it is commonly named air -- the word applying to the vaporous layer around the waters and within the land, shut in among the highest mountains, capable of holding thick clouds and tempestuous winds from South and from North. In so far as it is pure and entereth not into composition, but formeth the site and the enveloping space through which the compound body moveth on its course, we name it properly ether, a name which means its course (corso).  This ether, though in substance identical with the air which is stirred within the viscera of the earth, is nevertheless differently named. Just as that which is around us is called air, yet when it is in some sort part of us or at least hath a part in our composition -- as when it is found in our lungs, our arteries and other cavities and pores of our body -- it is called spirit. The same, when around a cold body, becometh condensed into vapour, but around a hot star it is attenuated like flame, which is sensible only if joined to a denser body which becometh ignited by the intense heat thereof. Thus the ether is of his own nature without determined quality, but it receiveth all the qualities offered by neighbouring bodies, and carrieth them with his own motion to the furthest limits of the horizon wherein such active principles have efficacy. Behold then, the nature hath been demonstrated to you of the worlds and of the heaven, so that not only can your present doubt be resolved,  but also innumerable others. And you are now equipped with a foundation for many true physical conclusions. And if some proposition hath hitherto appeared to you propounded but not proved, I shall leave it for the present to your own discretion. And if you are impartial, before you attain to discovering the supreme truth of such a proposition, you will deem it far more probable than the contrary view.
Albertino. Speak, O Theophilo, that I may hear thee.
Philotheo. Thus we have resolved the Sixth argument wherein, considering the contact of worlds in a single point, thou askest what object can occupy those triangular spaces so that it be neither of elemental nor of heavenly nature. But we postulate a single heaven in which the worlds have their own spaces, regions and convenient distances. It diffuseth throughout all, penetrateth all and it envelopeth, toucheth and is closely attached to all, leaving nowhere any vacant space; unless, indeed, like many others, thou preferest to give the name of void to this which is the site and position of all motion, the space in which all have their course. Or thou mayest call it the primal subject denoted by that word space, so as to ascribe unto it no limited position, if thou preferest by omission and logically to regard it as something distinct in our mind, but not in nature or in substance derived from being or body; so that nothing be understood to exist which hath not position either finite or infinite, either corporeal or incorporeal, either as a whole or by means of his parts: and this position can finally be no other than space, and the space cannot be other than void. If then we regard this space or void as persistent, we call it the ethereal field which containeth all worlds; if we regard it as a supporting substance, we call it the space, within which is the ethereal field with the worlds; and this space cannot be conceived as existing within another space. Behold then, we are under no necessity to feign new elements and worlds, unlike those who on the lightest provocation begin to name deferent orbs, divine substances, rarer and denser parts of celestial nature, quintessences and other fantasies, names lacking all meaning and truth.
To the Seventh argument we reply that the infinite universe is one, a single continuum, compound of ethereal regions and worlds. Innumerable are the worlds, and they should be understood to reside in diverse regions of the single universe, and to exist by the same law of nature as this world inhabited by us is understood and indeed doth reside in her own space and region thereof. This I expounded to Elpino during these last days, approving and confirming that which hath been said by Democritus, Epicurus and many others who contemplated nature with open eyes, nor made themselves deaf to her importunate voices.
Wherefore cease to spew out reason from your mind, struck with terror at mere newness; but rather with eager judgement weigh things, and, if you see them true, lift your hands and yield; or, if it is false, gird yourself to battle. For our minds now seek to reason, since the sum of space is boundless out beyond the walls of this world; what there is far out there, whither the spirit desires always to look forward, and whither the unfettered projection of our mind flies on unchecked. First of all we find that in every direction, everywhere, and on either side, above and below, through all the universe, there is no limit, as I have shown, and indeed the truth cries out for itself and the nature of the deep shines dear. 
Lucretius crieth out against your Eighth argument  which maintaineth that nature should encompass herself. For though we have tested this in worlds both great and small, it can be observed in none of them. For our bodily eye findeth never an end, but is vanquished by the immensity of space presented before it, and confused and overcome by the myriads of stars ever multiplying, so that our perception remaineth uncertain and reason is forced to add space to space, region to region, world to world.
Now in no way must we think it likely, since towards every side is infinite empty space, and seeds in unnumbered numbers in the deep universe fly about in many ways driven on in everlasting motion, that only this one world and heaven was brought to birth.... Wherefore, again and again, you must needs confess that elsewhere there are other gatherings of matter, such as this, which the ether holds in its greedy grip. 
He murmureth against the Ninth argument which supposeth, though it cannot prove, that there is not infinite passive power to correspond with infinite active power;  and that infinite matter cannot be patient nor infinite space make to itself a field; that consequently act and action cannot become conformable to the agent, and it may happen that though the agent impart the whole act, yet the whole act cannot be imparted. This latter opinion is the clearest possible contradiction to the former remarks. Well then hath it been said:
Moreover, when there is much matter ready to hand, when space is there, and no thing nor cause delays, things must, we may be sure, be carried on and completed. As it is, if there is so great a store of seeds as the whole life of living things could not number, since vigour is the same and nature abideth  who can throw together the seeds of things, each into their place, in like manner as they are thrown together here, it must needs be that you confess that there are other worlds in other regions, and diverse races of men and tribes of wild beasts. 
To the Next argument  we reply that there is no need of this courteous exchange of intercourse between the various worlds, any more than that all men should be one man or all animals one animal. And this apart from what we learn by experience, that it is best for the living creatures of this world that nature hath distributed their diverse kinds throughout seas and mountains. And if by human artifice there hath befallen traffic among them, good is thereby not so much added to them as removed, since communication tendeth rather to redouble vices than to augment virtues. Wherefore rightly the Tragic Muse lamenteth:
To the Tenth argument  the reply is as to the Fifth. For each world in the ethereal field occupieth his own space, so that one toucheth not nor thrusteth against the other; but they pursue their courses and are situate at such distance that contraries destroy not but rather comfort one another.
The Eleventh asserteth that Nature having multiplied by definition and division of matter, entereth on this act only by the method of generation, when the individual as parent produceth another individual. We reply that this is not universally true. For by the act of a single efficient cause there are produced from one mass many and diverse vessels of various forms and innumerable shapes. I leave aside that if there should come to pass the destruction of a world followed by the renewal thereof, then the production therein of animals alike perfect and imperfect would occur without an original act of generation, by the mere force and innate vigour of Nature.
Your Twelfth and Last argument maintaineth that because this or another world is perfect, therefore no further worlds are required. I reply that these are certainly not required for the perfection and subsistence of our own world, but that for the subsistence and perfection of the universe itself an infinity of worlds is indeed necessary. It therefore followeth not from the perfection of this or of those that those or this be less perfect; for this world even as those others, and those others even as this, are made up of their parts, and each is a single whole by virtue of his members.
Albertino. Thy noble countenance, O Philotheo, shall not be denied me by the voice of the mob, the indignation of the vulgar, the murmuring of fools, nor by the displeasure of satraps, the folly of the crazy, the foolishness of blockheads, the betrayal of liars, the complaints of the malicious nor the backbiting of the envious,  nor shall they deprive me of thy divine conversation. Persevere, my Philotheo, persevere. Do not lose heart nor retire, though the great and solemn senate of foolish ignorance threaten thee with many complots and cunning shifts and seek to destroy thy divine enterprise, thine exalted task. For be thou assured that at the last all will see as I now see, and all will acknowledge that it is as easy for everyone to praise thee as it is hard for them all to teach thee. For all (if they be not wholly perverse) will with good understanding deliver favourable verdict concerning thee, just as at last everyone cometh to be taught through the mild mastery of the mind, for only by dint of our own mind may we become possessed of the treasures of mind. And since there is in the minds of all a certain natural holiness enthroned in the tribunal of the intellect and exercising judgement between good and evil, between light and darkness; so it will happen that through the private meditations of each individual, there shall be aroused faithful and just witnesses and defenders in thy cause; and they who make not themselves thy friends, but blockishly seek the defence of gloomy ignorance, and as approved sophists remain thy steadfast and stiffnecked adversaries, these will feel within themselves the hangman and executioner, thine avenger; for the more they conceal him within the depth of thought, the more he will torment them. Just so the infernal Worm based on the bristling hair of the Furies, seeing that his design against thee is frustrated, will furiously turn on the hand or the breast of his impious factor, and will deal unto him that death which he may spread who scattereth the Stygian poison where the sharply pointed teeth of such a reptile have bitten.
Proceed to make known to us what is in truth the heaven, what in truth are the planets and all the stars; how the infinity of worlds are distinguished one from the other, how an infinite Space is not impossible but is necessary; how such an infinite effect beseemeth the infinite Cause. Reveal to us the true substance, matter, act and efficient cause of the whole, and how every sensible and composite object is built up from the same origins and elements. Convince our minds of the infinite universe. Rend in pieces the concave and convex surfaces which would limit and separate so many elements and heavens. Pour ridicule on deferent orbs and on fixed stars. Break and hurl to earth with the resounding whirlwind of lively reasoning those fantasies of the blind and vulgar herd, the adamantine walls of the primum mobile and the ultimate sphere. Dissolve the notion that our earth is unique and central to the whole. Remove the ignoble belief in that fifth essence. Give to us the knowledge that the composition of our own star and world is even as that of as many other stars and worlds as we can see. Each of the infinity of great and vast worlds, each of the infinity of lesser worlds, is equally sustained and nourished afresh through the succession of his ordered phases. Rid us of those external motive forces together with the limiting bounds of heaven. Open wide to us the gate through which we may perceive the likeness  of our own and of all other stars. Demonstrate to us that the substance of the other worlds throughout the ether is even as that of our own world. Make us clearly perceive that the motion of all of them proceedeth from [the impulse of] the inward soul: to the end that illumined by such contemplation we may proceed with surer steps toward a knowledge of nature.
Philotheo. What meaneth it, O Elpino, that Doctor Burchio hath not so speedily nor indeed ever consented with us?
Elpino. It is proper to vigilant wit that by seeing and hearing little he may consider and understand much.
Albertino. Although it hath not yet been vouchsafed to me to see the whole body of the shining planet, I can yet perceive by the rays diffused through the narrow slits in the closed windows of my mind, that this is no artificial brightness or sophist lamp, nor proceedeth from the moon or any lesser star. I prepare for a yet greater understanding in the future.
Philotheo. Your further friendship will be most acceptable.
Elpino. Then let us to supper.
End of the Five Dialogues Concerning
the Infinite Universe and Worlds.