 Hi, my name is Monty Johnson. I teach philosophy at the University of California, San Diego, and this is the fourth of six lectures on Lucretius, this one about sensation, illusion, thought, and desire in De Rerum Natura Book Four, and I'm using the translation of Cyril Bailey, which is available in the public domain through the Internet Archive. Now Think of where we are in the overall structure of this epic didactic poem. We've already proven the existence of an infinite number of atoms moving in an infinite void space and them getting entangled and colliding to form complexes and compounds, which themselves combine to form complex objects that are big enough for us to see and perceive. And some of these objects are living and have souls. All this has been explained and shown. Now we move on in book four to discuss higher psychological faculties like sensation, desire, and thought. So we've moved from the microscopic level of atoms and void to the level of psychology discussing the human soul senses in the mind. And we're using the physical assumptions and propositions, basic propositions of atomism to draw out some macroscopic implications for phenomena that we see and perceive, and also ethical implications for them because of how these things affect our desires. And so we move into the adulthood of the figure past the midway point between the birth with which the overall poem opens and the death with which it ends, and we move on to the complicated subject of human sensation and desire. Now book four, it's basic outline. The first 50 or so lines are the introduction. Here we have a reiteration of the poet's mission and the therapeutic purpose of the work and a summary of the preceding book in an overview of the contents of the present one. The 1000 lines of argument present a materialist and atomist account of sensation that it occurs through contact of sensible objects with sense organs gives an account of all five senses plus thought of sex, nutrition, motility, sleep, dreams, and sexual desire showing how they can all be explained on a materialist basis. And in the finale, there's an ethical attack on passionate love and an exhortation to self control and the limitation of sexual desire. Now, the introduction or poem to this book is especially problematic because there's repetitious material here. First, the exhortation to philosophy is here from book one, which describes the therapeutic purpose of the work and offers a comparison between medicine and philosophy is repeated here, including the lines about coding the cup of bitter medicine of philosophy with the sweet honey of poetry. There are also two different versions included here of the summary of the previous chapters, one of them summarizing the material from book two, the other summarizing the material from book three. This is led and this is some of the strongest this is led some interpreters and this is the strongest evidence for the idea that the poem was left unfinished. I suspect all this repetitive material and especially two different versions of the introduction, which presumably the second description of the previous book is the true one if book, the present book is correctly positioned as book four should be describing the context contents of book course, the contents of book two preceded book three so it's useful to have that reminder of the contents of that book anyway. Now the arguments in book four to give an overview of them the basis of all sense perception is material objects called simulacra, which are translator Bailey translates as idols other translators use the idea of images. These material objects make contact with our sense organs, and he's most interested and most keen to describe phenomena of sight and vision, including optical illusions, and describe how the simulacra are the basis for those kinds of sensations, but he also explains hearing taste smell and even thought on the same basis. And in fact he takes touch to be the most fundamental kind of sensation and every modality of sense to be a form of touch because the ultimate explanation for all sensation, of course, is about contact and collision of atoms in void. So after explaining sensation he moves on to explain other vital functions on a materialist basis as well, including nutrition, voluntary motion, sleep and dreams and sexual desire. And there's an amazing kind of build up and then finally climax almost literally in the part on sexual desire, where we move through all of the five senses into a description of how nutrition affects us and the kinds of desires we have for food and drink that are manifest in hunger and thirst and how that compels us to voluntary motion of our limbs and then a description of how the voluntary motion of our limbs slows down and stops and sleep where we still have dreams and so still have some kind of sensation or recollection of these simulacra and idols. And then among those idols and simulacra of course are the images of that arouse sexual desire and so the account of sexual desire comes at the end of the entire description of sensation and perception as if it's the ultimate end and outcome of the capability for sensation. Now the overall and detailed argument depends on accepting the view that small material bodies simulacra or idols are emitted from basically all parts of sensible objects but especially the outermost surfaces of them. And to convince us of this Lucretius points out that many objects emit scattered particles from themselves like wood, burning wood emit smoke, fire gives off heat, snakes and grasshoppers shed to coats. Now since these larger bodies are sloughed off of smaller objects then it's plausible to think that smaller and thinner bodies like these simulacra are might constantly be being sloughed off of larger objects like whole animals or human beings. And the idea is that the outermost layer of atoms making up the body has nothing impeding its departure so it's projected outward in all directions followed by the next layer of atoms which itself becomes the outermost and this process is happening continually. And colors are being conveyed to the eyes from the very surfaces of objects in this way as when colors are thrown off of awnings in a large theater and sort of projected out into space off of the material cloth themselves. Now when particles are emitted from deep inside of objects as smoke from wood then the color is darkened because of deviation in its trajectory but when they come from the outermost surface of objects and in straight lines then there's nothing to impede them and this is why vivid colors are conveyed. And Lucretius frequently appeals to the phenomena of mirrors in order to show that material objects must be thrown off of sensible objects that are reflected back to the sense organs from the mirror. Now these idols are extremely small but they can still be caught up in their transmission from the objects to our sense organs. So he says they're much smaller than the smallest visible part of any animal in fact they're one atom thick and so they how can they be have such an effect on our senses well it's comparable to the power of the effects of things like perfumes or incense when we can't see the particles affecting us but nonetheless we can smell them or detect them in some other way. We can't see the particles that we taste but they still affect our organs and they are transmitted sort of instantaneously to us and they can affect and alter our perception very rapidly. He says like images in clouds do which seem to instantly form and reform into different shapes a ship a house a face and so on and affect us instantly. Now there are three different possibilities in the transmission of these idols or simulacra from the objects to our sense organs. They can travel through certain bodies that have a lot of void and a lot of pores like the air or like glass and thus those media are we say transparent or they can be blocked and smashed up by solid and rough objects like stone or wood. And this is why we say those are opaque we can't see objects that are behind stone or wood walls because the idols that are being transmitted from the sensible objects in the next room get smashed up and blocked by these opaque objects. But another option besides transparency and opacity is when the idols come streaming back from the surface of an extremely smooth surface like a mirror or a pond. Such surfaces contain insufficient pores to be traveled through like transparent objects but they're too smooth to smash the simulacra or idols and so the image itself is cast back in the same direction. Now the idols are being transmitted extremely rapidly essentially the speed of light or even faster they move he says at the same roughly the same speed as the sun's light and heat are transmitted. And again compare how quickly images and clouds can be formed and reformed or how quickly something that's even very far away in outer space like a star can be immediately reflected in a pool of water or a mirror. If you if you put it in view and so that means they must be transmitted at the speed of light or very fast and how can they move so quickly well because they're so small and so light. So they don't collide with any other ambient bodies in the atmosphere because they are so small and they weigh so little there is nothing to stop them from moving as fast as possible essentially like atoms in void. Another reason they move so quickly is that they're emitted from the outermost surfaces of things not from their inner parts which would take longer and slow them down in the transmission instead they move directly from those surfaces to the surfaces of the sense organs. Now all sensation is thus treated as a kind of touch because in the Epicurean theory of perception all sensation is described as a kind of impression or contact between the atoms that are emitted from the surfaces of the objects and the atoms that comprise the sense organs. So there always has to be some kind of contact at basis for any form of sensation to happen and this applies as we've just seen to seeing because seeing occurs when idols or simulacra are transmitted from the outermost surfaces of objects to the surface of the eyeball. But the same process applies to smelling tasting hearing and so forth in these cases atoms are emitted or flowing from the surfaces or the internal parts of objects and they make contact with the atoms come constituting our noses tongues ears and so forth and the result of those combinations and juxtapositions are the alterations of senses that we perceive. So to go into a bit more detail into each one as he does beginning with seeing again the theory is that images are being emitted from the surfaces of the object but here Lucretius adds the detail that they move the air between the objects and our eyes so the eyes then receive an impression from the imprinted air. And Lucretius tries to explain why distant objects appear less distinct to us by appealing to the fact that the intermediary air is more disrupted there's more room for disruption so the intermediary air blocks and distorts the imprint so they don't appear the visible object doesn't appear as distinctly. Now of course we cannot perceive a single idol or simulacrum just as we can't perceive a single atom of wind or a single atom of cold or of a solid object like a stone we can't perceive single atoms at all. We need enough of them collected and enough of them inundating us to activate the alteration of the atoms in our sense organs in order to have the experience. And Lucretius offers an extensive discussion of mirror images including accounting for why mirror images are reversed and what happens to images when they're reflected through multiple mirrors and so forth and all of this according to the theory of idols or simulacra. And he goes into enormous detail on optical illusions and the reason he spends so much time on this is more or less clear because they are a big challenge to the Epicurean theory of perception. Again the Epicureans identify perception with sensation and reduce all sensation to touch claiming that ultimately collisions of atoms transmitted from sensible objects with atoms constituting these sense organs are what constitute the alteration of sensation and less perception. But they build an entire theory of knowledge on top of that entirely objective process. So in theory every sensation is true insofar as it's just a reception of the object it was admitted from into the objects that constitute my sense organs. So when things end up other than their objects actually are there is a problem and this needs to be explained and so Lucretius goes into detailed explanations about phenomenon like glare and excessively bright objects, yellowed or pale colors, lightened or darkened objects, square buildings appearing around at a distance, shadows, motion after effects, horizon and vanishing effects, why ores appear bent in water, why you get double vision when you apply pressure to the lower part of the eye and of course dream images. All of these effects he says have naturalistic explanations according to the theory of idols already outlined. And although they seem to threaten the credibility of the senses in fact they do not and reason can resolve this deception of the senses. In fact it's the mind that's been the cause of the deception and how it's interpreted the senses and if you look at it correctly the senses have always reported exactly what the objects are there's nothing else they could do. And again this is critically important for Epicureans because of their epistemology which holds that sensation is the criterion of all truth. They hold that knowledge is possible contrary to skeptical views they say that it is possible to have knowledge. If anyone argues that nothing can be known then he refutes himself since he declares that he himself knows nothing. But suppose it's granted even to such a skeptic that he knows that he knows nothing. How does he distinguish knowing from not knowing that is how does he distinguish true from false and certain from doubtful. And Epicureans answers that there's no other means for distinguishing these things true or false other than the senses. Quoting Lucretius you will find that the concept of the true is born first from the senses and that the senses cannot be refuted. So reasoning can't refute the senses because reasoning is entirely based on the senses and one mode of sensation cannot refute another mode of sensation. So hearing can't refute seeing and seeing can't refute tasting and reasoning can't refute any of those individual senses. So each of the senses must be true or as Lucretius puts it therefore whatever they have perceived on each occasion is true. So it's better in each case to determine how reasoning or the mind is at fault than to find fault with the senses. Since the senses are the foundation of all reason and if they are threatened then reason itself is threatened. And reasoning based on false sense data is like a house built with flawed measurements. It's structurally unsound and liable to collapse that is it's not secure knowledge. So every sense is veritical that is every sense is true and perceives its own object and so each of them must be given their own accounts. So he moves on to accounts of the other sense modalities which I will pass through relatively quickly. Beginning with hearing sounds voices and echoes are all effects of bodies for which a materialist explanation can be given. They in turn affect our sense organs and then other parts of our bodies. Lucretius goes into a lot of detail about the effects of spoken voices on audiences. There's an outsize attention paid to that particular aspect of hearing. Apparently he's thought very deeply about the rhetorical and poetical aspects of speech and sound. And he does give an interesting account of why sounds can pass through objects that are impenetrable by visible objects and that's because they can somehow move through sinuous and tortured passages that are between the object and the sense organ without getting smashed up while the thin and tenuous visible idols must travel in straight lines and tend to become smashed up whenever there are passages that turn in their way. Now tasting is explained in terms of food particles being squeezed out in the mouth and distributed across the tongue and palate. All of it is just material bodies interacting with other bodies when the particles are smooth. There's a sweet sensation because they pleasantly stroke all around the moist sweating vault above the tongue but when they're rough they prick and tear it in onslaught and this is what produces a bitter taste. So we can explain all the various kinds of taste by describing the effects of bodies of a certain shape on the bodies that constitute the sense organs. Now Lucretius here digresses to explain why different foods are good for different creatures because different creatures have different constitutions and the food is constituted differently and not every combination is possible. Not every combination is healthy or harmful for different animals. Different things are healthy or harmful and thus they taste differently and for the same reason taste differs in the same person when they're sick because their sense organs are constituted slightly differently than the same kind of object interacts with a differently constituted sense organ thus giving rise to a different kind of sensation. Smelling too is of course based on a theory of particles which stream from different objects into the sense organ of our nose. Smells are not transmitted as far as sounds or images because they are emitted from the depths of things and they have more difficulty because they have to travel through more tortured paths to reach their sense organs. They also consist of larger particles and sounds and so they more easily get caught up in solid bodies like walls and can't be transmitted through them. Smells affect creatures differently because the particles differ in shape and indicate potentially good or bad effects on their health thus bees are attracted to honey, vultures are attracted to carrion and so on and in general different animals react differently to different objects because the particles they emit interact differently with their own differently configured sense organs so lions fear cocks because there is something about how they appear that actually hurts and tears at the eyes of the lion and possibly the other kinds of particles being emitted from it also interact in a bad way that's painful and so this explains their avoidance behavior. Now the account of thought is really an account of how imagination is possible and it's explained according to this theory of idols or simulacra which gets extended to the effect on the mind or animus which was the subject of discussion in book 3. Thought ends up being a kind of image making or imagination. It's really about calling to mind or focusing on certain idols or simulacra or certain combinations of them. We're just rearranging them and giving them various kinds of focus and attention. The idea is that there are innumerable idols that are constantly moving in all directions through the void and they can become entangled as they're transmitted to our sense organs and because they're ultra fine they pass beyond the sense organs even the organs of vision and reach deeper into the body and the spirits as far as the animus which is deep within the chest. Now this is used as a basis to explain why people imagine things like mythological animals, centaurs. They have idols of humans and idols of horses and somehow these have become mixed up in colliding either in the medium of air or within the sense organs of the subject so that a half man half horse is conceived. Of course no actual centaur ever existed and that's why there's never any direct perception of them. But all imaginary creatures have some basis in recombination of actual sensations. Now a couple of questions about imagination and thought that Lucretius addresses. First, how can the images be imagined to move? After all, all we receive is, as it were, a set of static images that are constantly flowing off of the surfaces of the objects. The appearance of motion in both dreams and imagination that these aren't just static images but they're moving he describes as a kind of animation due to rapid succession of the images since each image is at a slightly different posture or position than the illusion of moving is produced. And he also offers to explain how the mind can think whatever at once it will and spontaneously produce an image of it, you know, think of an elephant, you can immediately do that and you can even imagine an elephant moving and walking across the plane. How is this possible? He says that in any period of time, including a temporal minimum of just a moment, there are in the mind, what we would call I guess the subconscious mind, innumerable images lurking and lying ready to be focused on by the mind. We have this vast reservoir that are constantly flowing into a pool of them. They're so small and ultra fine they can all be collected in this area of the mind in the chest. But because they're so small, the mind can't apprehend them clearly unless it concentrates or focuses attention on them repeatedly. And that's why if we have, you know, more experience, we can find them and focus on them more easily. But in sleep, they also pass for our mind. But since we can't use the other senses or our memory to judge and check them, they appear as if they're really happening. And that's why we can't tell that we're dreaming. And then when we're awake, our conscious attention is so flooded with the things that we actually are sensing and actively perceiving and calling to mind with our imagination and memory. It blurrs out any of those subconscious images. Now, a small digression on the natural history of the senses. Lucretius argues that the natural organs existed prior to their current uses by contrast to artificial tools which are designed and created after a purpose has already been conceived of them. So nothing is born in us for the sake of its use. Rather, that which is born creates the use of its senses and its limbs. So the eyes came to be before sight and the tongue before speech and the hand before grasping. And somehow the tongue was put to use by a creature in producing speech. It's not that some intelligent designer had conceived of speech and this would be a good idea and so designed to the tongue so that it could speak. Now, by way of contrast, murdering and fighting existed long before swords and arrows, dodging existed before shields and sleep existed before beds. These artifacts were produced for the sake of those natural uses, but they are in a different category from the natural senses and limbs which were not designed and weren't recombinations of matter deliberately put together for the sake of those uses. Now, the next vital function that Lucretius discusses is nutrition. Drinking and eating basically replenish this material that's constantly being sloughed off and lost from the body by this constant emission of idols, sounds, odors and so forth that we're throwing off and losing from the surface of our body. We need to sort of replenish that from the inside and eating fills up interstitial voids whose continuous growth in the body causes this sensation, this desire of hunger. And similarly, drinking provides fluid to help cool and extinguish the body because there's this heat in our stomach that sort of cooks our food and it will produce a scorching effect and gradually dry us out causing thirst unless we provide fluid to cool and extinguish it. And that's why we have a desire for thirst. So these primary desires for hunger, thirst and things like this can be explained in terms of the material lacks and voids within us. Now, the next thing to be described is how we can voluntarily move ourselves in order to cope with this hunger and thirst. That is, how can we, how can we feeling thirst move towards water in order to drink it or feeling hunger move towards food in order to eat it. And in general, if you think about it, and it's still a pretty good question, how is it that we can move our limbs at will? If we think about something that we desire, we're capable of moving towards that object, but how can something as small and insignificant as a thought move our large and weighty bodies? Well, Lucretius provides a fascinating mechanistic explanation. Now, by mechanistic explanation, I mean that his explanation is modeled on the way that the science of mechanics explains the working of machines. Lucretius himself doesn't provide an explanation of how any machines work, like pulleys, rudders, sails, etc. But he provides explanations of other phenomena, biomechanical phenomena, modeled on those mechanical phenomena. So the basic mechanism is like this. So an image makes an impression on my mind, for example, an image of chocolate cake. Next, I formulate a will to eat that chocolate cake. So I foresee my doing it. I combine an image of me moving towards the cake and eating the cake. And this foresight, this thought, which is again within the soul, the smallest of the atoms that makes up the soul body compound. This soul atom strikes the animal spirits, the larger animal spirits within the body, which it's easy to do because the mind or animus is closely connected to the spirit. And the spirit atoms then strike the even larger air, soul air atoms, and then the air pushes out to impact with the rest of the body, the outer limbs of the body, so that the whole mass is pushed and moved, as he says, as a ship is by sails and wind. So the tiny image moves the slightly larger soul atoms, which move the slightly larger spirit atoms, which move the slightly larger air atoms, which hit against the, as it were, sails at the ends of our limbs, which then move the limbs. Then the limbs are able to move towards the chocolate cake or the object as intended and eat it, thus satisfying this desire for cause by hunger or expanding voids within the body. And Lucretius compares all this to the way rudders and pulleys can cause very small forces to be amplified and have large effects, just as invisible wind particles are able to move a large ship. So these ultra fine image particles are able to, by causing this kind of chain reaction of the soul, spirit, and air particles within us move a large and weighty body. And so he gives an entirely materialistic mechanistic explanation of voluntary motion. Interestingly, no mention of the swerve here in earlier discussion of voluntary motion in book two described the swerve and then gave a similar mechanistic but shorter mechanistic account of how motion works. So we can infer that a new swerve is apparently not necessary to explain every voluntary motion because we've just had an explanation of voluntary motion that occurs as a result of a chain reaction from an image to a movement of the overall body. Now, after the discussion of how the body moves, we need a discussion of how the body stops moving and an explanation of why it goes into sleep, which we spend such a great portion of our lives doing. Sleep, he says, involves the departure of some of these spirit atoms so crucial to moving the body in voluntary motion. Some of these spirit atoms depart and dissipate from the body and others retreat to the innermost parts of the body so that the outermost limbs remain inactive. Of course, only part of the spirit leaves. If all of it left, the result would be paralysis and death. But the overall cause of sleep is due to the fact that our bodies are constantly being buffeted by air from the outside. Our skin is partly protective against this, but not only that, when we breathe in the same air beats on the inner parts and being beaten both internally and externally, the structures and passageways of the limbs collapse. And so the balance of body and mind atoms becomes disordered when the part of the spirit retreats and draws inward. It's no longer in communication with the outer parts of the limbs and so it can't move them and the limbs being unsupported then relax. And he says, food has a similar effect on internal buffeting of organs and that's why eating a lot can cause sleepiness. Now after explaining sleep, it's natural next to explain dreams. Dreams again are given a materialist explanation. He points out they mostly relate to things we sense in waking life and things we do in waking life thus lawyers dream of pleading in court and generals dream of engaging in battle. Sometimes we can even be so conditioned to seeing or hearing things that we see images or hear sounds of them even when awake. As in daydreaming or deep intense kinds of imagination or visualization, dreams are very similar to this. Animals also dream, horses he says, dream of their races, dogs of the chase, birds of being pursued, just as kings dream of victory. People even talk in their sleep about their secrets from waking life. Now dreams that we have about falling or being thirsty or wetting the bed involve vivid images of things encountered when awake. So all of these kinds of dreams are explained as being the persistence of images taken into the sense organs when we are awake and running before our minds when our minds are not being clouded out by other kinds of sensation, memory, imagination and thought. The final kind of dream he gives an explanation of is wet dreams, which he says occur once seed that stirred up at the age of full growth. When images from chance bodies fly from abroad come to the mind in dreams, then they cause a release of this seed. And this is the transition between the topic of dreams and the final climactic topic of the book for the discussion of sexual desire and procreation. Again, we have a purely materialist and atomistic description of it. It's amazing to think that this explanation has been built in a continuous succession going from sensation up through thought, nutrition, sleep, dreams, imagination and now sexual desire. And so he says that sexual desire is caused by seed being stirred up from within the body and withdrawn from all the limbs and all the different members, gathers in the region of the loins and arouses the body's genital parts, which become excited and swell. And this produces a desire to emit the seed that is accumulated and quote, the body seeks that which has wounded the mind with love. So he imagines that there is that the sense organs have been affected by an image of a boy or a girl who's described as inflicting a wound of love upon them. And the effect of this wound of love is that there's a burning desire to eject the seed in that direction just as blood from a wound jets in the direction of the blow that inflicted it. So desire to emit the seed is directed at the source of the wound of love. This Lucretius says is our Venus. And of course, he puts it very beautifully and poetically and I have not done any justice to that poetry and in fact I'm discussing the most prosaic aspect of it how it relates to this underlying materialist atomistic thesis. And here when he says this is our Venus, it calls to mind the opening of the entire poem, the invocation to Venus, Venus being the Roman version of the Greek goddess Aphrodite, the goddess of erotic passionate love and sexual intercourse creation and reproduction has been reduced in this materialist account to certain bodies affecting certain other bodies and swelling and being admitted and then colliding in various ways. And so the goddess there has been, as it were, obviated by an naturalistic materialistic atomistic Epicurean description of the cause and effect of sexual desire. This leads then into moralizing about sexual desire and procreation and Lucretius warns against passionate love and advises that one should avoid and even scare away whatever feeds passionate love. One should in fact he says find persons with whom one is not in love in order to have sex with so that the wounds of love will not be worsened. That leads to a kind of madness. So he gives exactly the contrary advice that our parents do. Our parents say only have sex with somebody you're in love with. Lucretius says only have sex with someone you're not in love with because then you'll satisfy this desire to omit the seed without the madness producing passionate wound of love being expanded and affecting you. Lucretius asserts that people who are not afflicted with love can actually have more gratifying sexual pleasure and he describes passionate love as being frenzied and mixed up with pain. And furthermore, passionate love causes desires that can't ever be satisfied and the madness produces all imaginable vices, luxury pangs of conscious jealousy and so on. Unsuccessful love is of course even worse and should be avoided at all costs. Passionate love makes one overlook grave faults of the beloved and has all kinds of distortive effects. He does point out that women can be just as passionate and derive as much pleasure as men can from sex and he seems to encourage that. Now the book ends with an account of heredity, the final effects of passionate love on procreation. And he presents briefly the idea that the male and female seed is mingled and transmitted from generation to generation. And he uses the same kind of theory to explain barrenness, there must be incompatible shapes that somehow fail to mix in necessary ways. And he actually recommends certain sexual positions that he suggests may increase or decrease the chance of conception. And he concludes by discussing how one may come to love a plain woman and thus avoid the snares of passionate love. So ends with an ethical Epicurean extrapolation about limitation of our desires built up on top of an entirely naturalistic thesis stemming from the smallest imaginable kind of atoms constantly being transmitted in every direction in the void to their ultimate effects on our desire and behavior and reproduction.