I would here willingly have proceeded to exhibit the whole chain o truths which I deduced from these primary but as with a view to this i would have been necessary now to treat of many questions in disput among the earned, with whom I do not wish to be embroiled, I believ that it will be better for me to refrain from this exposition, and onl mention in general what these truths are, that the more judicious ma be able to determine whether a more special account of them woul conduce to the public advantage. I have ever remained firm in m original resolution to suppose no other principle than that of which have recently availed myself in demonstrating the existence of God an of the soul, and to accept as true nothing that did not appear to m more clear and certain than the demonstrations of the geometers ha formerly appeared; and yet I venture to state that not only have found means to satisfy myself in a short time on all the principa difficulties which are usually treated of in philosophy, but I hav also observed certain laws established in nature by God in such manner, and of which he has impressed on our minds such notions, tha after we have reflected sufficiently upon these, we cannot doubt tha they are accurately observed in all that exists or takes place in th world and farther, by considering the concatenation of these laws, i appears to me that I have discovered many truths more useful and mor important than all I had before learned, or even had expected to learn

But because I have essayed to expound the chief of these discoveries i a treatise which certain considerations prevent me from publishing, cannot make the results known more conveniently than by here giving summary of the contents of this treatise. It was my design to compris in it all that, before I set myself to write it, I thought I knew o the nature of material objects. But like the painters who, findin themselves unable to represent equally well on a plain surface all th different faces of a solid body, select one of the chief, on whic alone they make the light fall, and throwing the rest into the shade allow them to appear only in so far as they can be seen while lookin at the principal one; so, fearing lest I should not be able to compens in my discourse all that was in my mind, I resolved to expound singly though at considerable length, my opinions regarding light; then t take the opportunity of adding something on the sun and the fixe stars, since light almost wholly proceeds from them; on the heaven since they transmit it; on the planets, comets, and earth, since the reflect it; and particularly on all the bodies that are upon the earth since they are either colored, or transparent, or luminous; and finall on man, since he is the spectator of these objects. Further, to enabl me to cast this variety of subjects somewhat into the shade, and t express my judgment regarding them with greater freedom, without bein necessitated to adopt or refute the opinions of the learned, I resolve to leave all the people here to their disputes, and to speak only o what would happen in a new world, if God were now to create somewher in the imaginary spaces matter sufficient to compose one, and were t agitate variously and confusedly the different parts of this matter, s that there resulted a chaos as disordered as the poets ever feigned and after that did nothing more than lend his ordinary concurrence t nature, and allow her to act in accordance with the laws which he ha established. On this supposition, I, in the first place, describe this matter, and essayed to represent it in such a manner that to m mind there can be nothing clearer and more intelligible, except wha has been recently said regarding God and the soul; for I even expressl supposed that it possessed none of those forms or qualities which ar so debated in the schools, nor in general anything the knowledge o which is not so natural to our minds that no one can so much as imagin himself ignorant of it. Besides, I have pointed out what are the law of nature; and, with no other principle upon which to found m reasonings except the infinite perfection of God, I endeavored t demonstrate all those about which there could be any room for doubt and to prove that they are such, that even if God had created mor worlds, there could have been none in which these laws were no observed. Thereafter, I showed how the greatest part of the matter o this chaos must, in accordance with these laws, dispose and arrang itself in such a way as to present the appearance of heavens; how i the meantime some of its parts must compose an earth and some planet and comets, and others a sun and fixed stars. And, making a digressio at this stage on the subject of light, I expounded at considerabl length what the nature of that light must be which is found in the su and the stars, and how thence in an instant of time it traverses th immense spaces of the heavens, and how from the planets and comets i is reflected towards the earth. To this I likewise added muc respecting the substance, the situation, the motions, and all th different qualities of these heavens and stars; so that I thought I ha said enough respecting them to show that there is nothing observable i the heavens or stars of our system that must not, or at least may no appear precisely alike in those of the system which I described. came next to speak of the earth in particular, and to show how, eve though I had expressly supposed that God had given no weight to th matter of which it is composed, this should not prevent all its part from tending exactly to its center; how with water and air on it surface, the disposition of the heavens and heavenly bodies, mor especially of the moon, must cause a flow and ebb, like in all it circumstances to that observed in our seas, as also a certain curren both of water and air from east to west, such as is likewise observe between the tropics; how the mountains, seas, fountains, and river might naturally be formed in it, and the metals produced in the mines and the plants grow in the fields and in general, how all the bodie which are commonly denominated mixed or composite might be generate and, among other things in the discoveries alluded to inasmuch a besides the stars, I knew nothing except fire which produces light, spared no pains to set forth all that pertains to its nature,--th manner of its production and support, and to explain how heat i sometimes found without light, and light without heat; to show how i can induce various colors upon different bodies and other divers qualities; how it reduces some to a liquid state and hardens others how it can consume almost all bodies, or convert them into ashes an smoke; and finally, how from these ashes, by the mere intensity of it action, it forms glass: for as this transmutation of ashes into glas appeared to me as wonderful as any other in nature, I took a specia pleasure in describing it. I was not, however, disposed, from thes circumstances, to conclude that this world had been created in th manner I described; for it is much more likely that God made it at th first such as it was to be. But this is certain, and an opinio commonly received among theologians, that the action by which he no sustains it is the same with that by which he originally created it; s that even although he had from the beginning given it no other for than that of chaos, provided only he had established certain laws o nature, and had lent it his concurrence to enable it to act as it i wont to do, it may be believed, without discredit to the miracle o creation, that, in this way alone, things purely material might, i course of time, have become such as we observe them at present; an their nature is much more easily conceived when they are beheld comin in this manner gradually into existence, than when they are onl considered as produced at once in a finished and perfect state

From the description of inanimate bodies and plants, I passed t animals, and particularly to man. But since I had not as ye sufficient knowledge to enable me to treat of these in the same manne as of the rest, that is to say, by deducing effects from their causes and by showing from what elements and in what manner nature mus produce them, I remained satisfied with the supposition that God forme the body of man wholly like to one of ours, as well in the externa shape of the members as in the internal conformation of the organs, o the same matter with that I had described, and at first placed in it n rational soul, nor any other principle, in room of the vegetative o sensitive soul, beyond kindling in the heart one of those fires withou light, such as I had already described, and which I thought was no different from the heat in hay that has been heaped together before i is dry, or that which causes fermentation in new wines before they ar run clear of the fruit. For, when I examined the kind of function which might, as consequences of this supposition, exist in this body, found precisely all those which may exist in us independently of al power of thinking, and consequently without being in any measure owin to the soul; in other words, to that part of us which is distinct fro the body, and of which it has been said above that the natur distinctively consists in thinking, functions in which the animals voi of reason may be said wholly to resemble us; but among which I coul not discover any of those that, as dependent on thought alone, belon to us as men, while, on the other hand, I did afterwards discover thes as soon as I supposed God to have created a rational soul, and to hav annexed it to this body in a particular manner which I described

But, in order to show how I there handled this matter, I mean here t give the explication of the motion of the heart and arteries, which, a the first and most general motion observed in animals, will afford th means of readily determining what should be thought of all the rest And that there may be less difficulty in understanding what I am abou to say on this subject, I advise those who are not versed in anatomy before they commence the perusal of these observations, to take th trouble of getting dissected in their presence the heart of some larg animal possessed of lungs (for this is throughout sufficiently like th human), and to have shown to them its two ventricles or cavities: i the first place, that in the right side, with which correspond two ver ample tubes, viz., the hollow vein (vena cava), which is the principa receptacle of the blood, and the trunk of the tree, as it were, o which all the other veins in the body are branches; and the arteria vein (vena arteriosa), inappropriately so denominated, since it is i truth only an artery, which, taking its rise in the heart, is divided after passing out from it, into many branches which presently dispers themselves all over the lungs; in the second place, the cavity in th left side, with which correspond in the same manner two canals in siz equal to or larger than the preceding, viz., the venous artery (arteri venosa), likewise inappropriately thus designated, because it is simpl a vein which comes from the lungs, where it is divided into man branches, interlaced with those of the arterial vein, and those of th tube called the windpipe, through which the air we breathe enters; an the great artery which, issuing from the heart, sends its branches al over the body. I should wish also that such persons were carefull shown the eleven pellicles which, like so many small valves, open an shut the four orifices that are in these two cavities, viz., three a the entrance of the hollow veins where they are disposed in such manner as by no means to prevent the blood which it contains fro flowing into the right ventricle of the heart, and yet exactly t prevent its flowing out; three at the entrance to the arterial vein which, arranged in a manner exactly the opposite of the former, readil permit the blood contained in this cavity to pass into the lungs, bu hinder that contained in the lungs from returning to this cavity; and in like manner, two others at the mouth of the venous artery, whic allow the blood from the lungs to flow into the left cavity of th heart, but preclude its return; and three at the mouth of the grea artery, which suffer the blood to flow from the heart, but prevent it reflux. Nor do we need to seek any other reason for the number o these pellicles beyond this that the orifice of the venous artery bein of an oval shape from the nature of its situation, can be adequatel closed with two, whereas the others being round are more convenientl closed with three. Besides, I wish such persons to observe that th grand artery and the arterial vein are of much harder and firme texture than the venous artery and the hollow vein; and that the tw last expand before entering the heart, and there form, as it were, tw pouches denominated the auricles of the heart, which are composed of substance similar to that of the heart itself; and that there is alway more warmth in the heart than in any other part of the body--an finally, that this heat is capable of causing any drop of blood tha passes into the cavities rapidly to expand and dilate, just as al liquors do when allowed to fall drop by drop into a highly heate vessel

For, after these things, it is not necessary for me to say anythin more with a view to explain the motion of the heart, except that whe its cavities are not full of blood, into these the blood of necessit flows,--from the hollow vein into the right, and from the venous arter into the left; because these two vessels are always full of blood, an their orifices, which are turned towards the heart, cannot then b closed. But as soon as two drops of blood have thus passed, one int each of the cavities, these drops which cannot but be very large because the orifices through which they pass are wide, and the vessel from which they come full of blood, are immediately rarefied, an dilated by the heat they meet with. In this way they cause the whol heart to expand, and at the same time press home and shut the fiv small valves that are at the entrances of the two vessels from whic they flow, and thus prevent any more blood from coming down into th heart, and becoming more and more rarefied, they push open the si small valves that are in the orifices of the other two vessels, throug which they pass out, causing in this way all the branches of th arterial vein and of the grand artery to expand almost simultaneousl with the heart which immediately thereafter begins to contract, as d also the arteries, because the blood that has entered them has cooled and the six small valves close, and the five of the hollow vein and o the venous artery open anew and allow a passage to other two drops o blood, which cause the heart and the arteries again to expand a before. And, because the blood which thus enters into the heart passe through these two pouches called auricles, it thence happens that thei motion is the contrary of that of the heart, and that when it expand they contract. But lest those who are ignorant of the force o mathematical demonstrations and who are not accustomed to distinguis true reasons from mere verisimilitudes, should venture, withou examination, to deny what has been said, I wish it to be considere that the motion which I have now explained follows as necessarily fro the very arrangement of the parts, which may be observed in the hear by the eye alone, and from the heat which may be felt with the fingers and from the nature of the blood as learned from experience, as doe the motion of a clock from the power, the situation, and shape of it counterweights and wheels

But if it be asked how it happens that the blood in the veins, flowin in this way continually into the heart, is not exhausted, and why th arteries do not become too full, since all the blood which passe through the heart flows into them, I need only mention in reply wha has been written by a physician of England, who has the honor of havin broken the ice on this subject, and of having been the first to teac that there are many small passages at the extremities of the arteries through which the blood received by them from the heart passes into th small branches of the veins, whence it again returns to the heart; s that its course amounts precisely to a perpetual circulation. Of thi we have abundant proof in the ordinary experience of surgeons, who, b binding the arm with a tie of moderate straitness above the part wher they open the vein, cause the blood to flow more copiously than i would have done without any ligature; whereas quite the contrary woul happen were they to bind it below; that is, between the hand and th opening, or were to make the ligature above the opening very tight For it is manifest that the tie, moderately straightened, whil adequate to hinder the blood already in the arm from returning toward the heart by the veins, cannot on that account prevent new blood fro coming forward through the arteries, because these are situated belo the veins, and their coverings, from their greater consistency, ar more difficult to compress; and also that the blood which comes fro the heart tends to pass through them to the hand with greater forc than it does to return from the hand to the heart through the veins And since the latter current escapes from the arm by the opening mad in one of the veins, there must of necessity be certain passages belo the ligature, that is, towards the extremities of the arm through whic it can come thither from the arteries. This physician likewis abundantly establishes what he has advanced respecting the motion o the blood, from the existence of certain pellicles, so disposed i various places along the course of the veins, in the manner of smal valves, as not to permit the blood to pass from the middle of the bod towards the extremities, but only to return from the extremities to th heart; and farther, from experience which shows that all the bloo which is in the body may flow out of it in a very short time through single artery that has been cut, even although this had been closel tied in the immediate neighborhood of the heart and cut between th heart and the ligature, so as to prevent the supposition that the bloo flowing out of it could come from any other quarter than the heart

But there are many other circumstances which evince that what I hav alleged is the true cause of the motion of the blood: thus, in th first place, the difference that is observed between the blood whic flows from the veins, and that from the arteries, can only arise fro this, that being rarefied, and, as it were, distilled by passin through the heart, it is thinner, and more vivid, and warme immediately after leaving the heart, in other words, when in th arteries, than it was a short time before passing into either, in othe words, when it was in the veins; and if attention be given, it will b found that this difference is very marked only in the neighborhood o the heart; and is not so evident in parts more remote from it. In th next place, the consistency of the coats of which the arterial vein an the great artery are composed, sufficiently shows that the blood i impelled against them with more force than against the veins. And wh should the left cavity of the heart and the great artery be wider an larger than the right cavity and the arterial vein, were it not tha the blood of the venous artery, having only been in the lungs after i has passed through the heart, is thinner, and rarefies more readily and in a higher degree, than the blood which proceeds immediately fro the hollow vein? And what can physicians conjecture from feeling th pulse unless they know that according as the blood changes its natur it can be rarefied by the warmth of the heart, in a higher or lowe degree, and more or less quickly than before? And if it be inquire how this heat is communicated to the other members, must it not b admitted that this is effected by means of the blood, which, passin through the heart, is there heated anew, and thence diffused over al the body? Whence it happens, that if the blood be withdrawn from an part, the heat is likewise withdrawn by the same means; and althoug the heart were as-hot as glowing iron, it would not be capable o warming the feet and hands as at present, unless it continually sen thither new blood. We likewise perceive from this, that the true us of respiration is to bring sufficient fresh air into the lungs, t cause the blood which flows into them from the right ventricle of th heart, where it has been rarefied and, as it were, changed into vapors to become thick, and to convert it anew into blood, before it flow into the left cavity, without which process it would be unfit for th nourishment of the fire that is there. This receives confirmation fro the circumstance, that it is observed of animals destitute of lung that they have also but one cavity in the heart, and that in childre who cannot use them while in the womb, there is a hole through whic the blood flows from the hollow vein into the left cavity of the heart and a tube through which it passes from the arterial vein into th grand artery without passing through the lung. In the next place, ho could digestion be carried on in the stomach unless the hear communicated heat to it through the arteries, and along with thi certain of the more fluid parts of the blood, which assist in th dissolution of the food that has been taken in? Is not also th operation which converts the juice of food into blood easil comprehended, when it is considered that it is distilled by passing an repassing through the heart perhaps more than one or two hundred time in a day? And what more need be adduced to explain nutrition, and th production of the different humors of the body, beyond saying, that th force with which the blood, in being rarefied, passes from the hear towards the extremities of the arteries, causes certain of its parts t remain in the members at which they arrive, and there occupy the plac of some others expelled by them; and that according to the situation shape, or smallness of the pores with which they meet, some rathe than others flow into certain parts, in the same way that some sieve are observed to act, which, by being variously perforated, serve t separate different species of grain? And, in the last place, wha above all is here worthy of observation, is the generation of th animal spirits, which are like a very subtle wind, or rather a ver pure and vivid flame which, continually ascending in great abundanc from the heart to the brain, thence penetrates through the nerves int the muscles, and gives motion to all the members; so that to accoun for other parts of the blood which, as most agitated and penetrating are the fittest to compose these spirits, proceeding towards the brain it is not necessary to suppose any other cause, than simply, that th arteries which carry them thither proceed from the heart in the mos direct lines, and that, according to the rules of mechanics which ar the same with those of nature, when many objects tend at once to th same point where there is not sufficient room for all (as is the cas with the parts of the blood which flow forth from the left cavity o the heart and tend towards the brain), the weaker and less agitate parts must necessarily be driven aside from that point by the stronge which alone in this way reach it I had expounded all these matters wit sufficient minuteness in the treatise which I formerly thought o publishing. And after these, I had shown what must be the fabric o the nerves and muscles of the human body to give the animal spirit contained in it the power to move the members, as when we see head shortly after they have been struck off still move and bite the earth although no longer animated; what changes must take place in the brai to produce waking, sleep, and dreams; how light, sounds, odors, tastes heat, and all the other qualities of external objects impress it wit different ideas by means of the senses; how hunger, thirst, and th other internal affections can likewise impress upon it divers ideas what must be understood by the common sense (sensus communis) in whic these ideas are received, by the memory which retains them, by th fantasy which can change them in various ways, and out of them compos new ideas, and which, by the same means, distributing the anima spirits through the muscles, can cause the members of such a body t move in as many different ways, and in a manner as suited, whether t the objects that are presented to its senses or to its interna affections, as can take place in our own case apart from the guidanc of the will. Nor will this appear at all strange to those who ar acquainted with the variety of movements performed by the differen automata, or moving machines fabricated by human industry, and tha with help of but few pieces compared with the great multitude of bones muscles, nerves, arteries, veins, and other parts that are found in th body of each animal. Such persons will look upon this body as machine made by the hands of God, which is incomparably bette arranged, and adequate to movements more admirable than is any machin of human invention. And here I specially stayed to show that, wer there such machines exactly resembling organs and outward form an ap or any other irrational animal, we could have no means of knowing tha they were in any respect of a different nature from these animals; bu if there were machines bearing the image of our bodies, and capable o imitating our actions as far as it is morally possible, there woul still remain two most certain tests whereby to know that they were no therefore really men. Of these the first is that they could never us words or other signs arranged in such a manner as is competent to us i order to declare our thoughts to others: for we may easily conceive machine to be so constructed that it emits vocables, and even that i emits some correspondent to the action upon it of external object which cause a change in its organs; for example, if touched in particular place it may demand what we wish to say to it; if in anothe it may cry out that it is hurt, and such like; but not that it shoul arrange them variously so as appositely to reply to what is said in it presence, as men of the lowest grade of intellect can do. The secon test is, that although such machines might execute many things wit equal or perhaps greater perfection than any of us, they would, withou doubt, fail in certain others from which it could be discovered tha they did not act from knowledge, but solely from the disposition o their organs: for while reason is an universal instrument that i alike available on every occasion, these organs, on the contrary, nee a particular arrangement for each particular action; whence it must b morally impossible that there should exist in any machine a diversit of organs sufficient to enable it to act in all the occurrences o life, in the way in which our reason enables us to act. Again, b means of these two tests we may likewise know the difference betwee men and brutes. For it is highly deserving of remark, that there ar no men so dull and stupid, not even idiots, as to be incapable o joining together different words, and thereby constructing declaration by which to make their thoughts understood; and that on th other hand, there is no other animal, however perfect or happil circumstanced, which can do the like. Nor does this inability aris from want of organs: for we observe that magpies and parrots can utte words like ourselves, and are yet unable to speak as we do, that is, s as to show that they understand what they say; in place of which me born deaf and dumb, and thus not less, but rather more than the brutes destitute of the organs which others use in speaking, are in the habi of spontaneously inventing certain signs by which they discover thei thoughts to those who, being usually in their company, have leisure t learn their language. And this proves not only that the brutes hav less reason than man, but that they have none at all: for we see tha very little is required to enable a person to speak; and since certain inequality of capacity is observable among animals of the sam species, as well as among men, and since some are more capable of bein instructed than others, it is incredible that the most perfect ape o parrot of its species, should not in this be equal to the most stupi infant of its kind or at least to one that was crack-brained, unles the soul of brutes were of a nature wholly different from ours. And w ought not to confound speech with the natural movements which indicat the passions, and can be imitated by machines as well as manifested b animals; nor must it be thought with certain of the ancients, that th brutes speak, although we do not understand their language. For i such were the case, since they are endowed with many organs analogou to ours, they could as easily communicate their thoughts to us as t their fellows. It is also very worthy of remark, that, though ther are many animals which manifest more industry than we in certain o their actions, the same animals are yet observed to show none at all i many others: so that the circumstance that they do better than we doe not prove that they are endowed with mind, for it would thence follo that they possessed greater reason than any of us, and could surpass u in all things; on the contrary, it rather proves that they ar destitute of reason, and that it is nature which acts in them accordin to the disposition of their organs: thus it is seen, that a cloc composed only of wheels and weights can number the hours and measur time more exactly than we with all our skin

I had after this described the reasonable soul, and shown that it coul by no means be educed from the power of matter, as the other things o which I had spoken, but that it must be expressly created; and that i is not sufficient that it be lodged in the human body exactly like pilot in a ship, unless perhaps to move its members, but that it i necessary for it to be joined and united more closely to the body, i order to have sensations and appetites similar to ours, and thu constitute a real man. I here entered, in conclusion, upon the subjec of the soul at considerable length, because it is of the greates moment: for after the error of those who deny the existence of God, a error which I think I have already sufficiently refuted, there is non that is more powerful in leading feeble minds astray from the straigh path of virtue than the supposition that the soul of the brutes is o the same nature with our own; and consequently that after this life w have nothing to hope for or fear, more than flies and ants; in place o which, when we know how far they differ we much better comprehend th reasons which establish that the soul is of a nature wholly independen of the body, and that consequently it is not liable to die with th latter and, finally, because no other causes are observed capable o destroying it, we are naturally led thence to judge that it is immortal