Diogenes is something of a throwback—a Milesian kind of philosopher in a post-Parmenidean world. He is also an eclectic, borrowing not just from Anaxagoras and Leucippus (as T1 says, though our evidence for Leucippus is so slight that it is hard for us now to detect his influence), but from Heraclitus too, while his most important debt is to Anaximenes. But he writes clearly, and makes some original contributions. Above all, in F2 he announces his major new insight, which he thinks will allow him to reinstate monism instead of the pluralism of his immediate predecessors. This insight is that unless everything was essentially related (i.e. was made up of the same underlying stuff) nothing could interact and generation would be impossible.1 It makes no sense to Diogenes to say that, for instance, Empedocles’ four elements, randomly thrown together in certain proportions, can make up the things of this world: bone could not grow out of bone unless there was an underlying unity, and bone could not combine with other substances either unless there was an underlying unity. Like Empedocles and Anaxagoras, Diogenes believes that mixture and separation are responsible for the generation and destruction of things, but unlike them he holds that there is no plurality of elements or substances involved in the mixture and separation. It is tempting also to believe that Diogenes was attracted by the simplicity of his system, as opposed to the formidable complexity of Empedocles and Anaxagoras. We have no evidence as to how Diogenes got around the Eleatic strictures about change and motion, but he probably borrowed the concept of void from Leucippus.
Impressed (as Heraclitus and Anaximander were) with the regularity of large-scale events in the universe, Diogenes posited, like Anaxagoras, a guiding intelligence (F3), which he then went on to identify with air, for the reasons given in F4. Air turns out also to be his underlying stuff (F5).2If air is responsible for life, Diogenes seems to have argued, then it is divine, and since life manifestly displays the workings of intelligence, then air is or has intelligence. Intelligence and warmth are related, presumably because a corpse is cold and has no intelligence. Presumably the most powerful intelligence, that of the divine air itself, is warmest. One may guess, then, that the air close to the sun to which Diogenes refers in F5 is the primary, divine form of air; he may well, then, have been assuming a standard Presocratic universe of concentric spheres of the primary stuffs, with air on the outside controlling the universe as a whole, then fire, then water and earth. The idea that intelligence is warm air, combined with the idea that everything has air in different temperatures, cleverly allows Diogenes to distinguish not just between individuals, but between species, and between animate and (cold) inanimate objects. In T1 Theophrastus reports that Diogenes attributed all different modifications of air to condensation and rarefaction, as Anaximenes had done, but we can see from Diogenes’ own words that different temperature is of prime importance to him. If Theophrastus is right, then, perhaps Diogenes thought that compressed air was cooler or warmer than rarefied air.
Little is known of Diogenes’ cosmogonical, cosmological, astronomical, and meteorological views. It is distinctly possible that he was far less interested in them than in the workings of the human body. But there are a few attributions of such views to him (T2–6), which are self-explanatory. The rest of the testimonia, and one long fragment, are concerned with human physiology in some way or another. I omit some incidental remarks about embryology, but his theories of perception (T7) are remarkable in recognizing the importance of the brain (rather than the heart, the traditional Greek seat of perception), although he was not the first to do so: earlier in the fifth century Alcmaeon of Croton, a physician with Pythagorean philosophical leanings, had pinpointed the brain as the core of perception. The consistency with which he explains everything by means of air is also worth noting. He even went so far as to say that male sperm carries air: since air is the source of life, it has to be essentially involved in conception. In considering F8, an account of the veins running through the body, it is worth not just reflecting on the passage as a piece of early medical science (although the principles of symmetry and division into two seem to be as important as observation), but also remembering that for Diogenes, of course, these veins did not just carry blood, but air as well: blood, like semen (which was a product of blood), was aerated. Hence (as we see from T7) the intelligence of adult humans: air could be transported all through their bodies.
Diogenes is indeed the last of the Presocratics. Dissatisfied with Parmenides and post-Parmenidean pluralism, he simply ignored what he wanted to ignore and borrowed what he wanted to borrow, to create a neat synthesis. But this opens the door only to further refinements, not to innovative work such as the Milesians or Parmenides or Empedocles had undertaken. Where now could Presocratic philosophy go? At the same time, his evident interest in the workings of the human body shows that Diogenes was truly a thinker of the late fifth century, emphasizing the individual over the cosmos, and the physical rather than the metaphysical.
T1 (DK 64A5; KRS 598) Diogenes of Apollonia was more or less the last of those who made a study of natural science. He cobbled together most of the ideas of his book from either Anaxagoras or Leucippus. He is another one who says that everything is made up of air, which is boundless and eternal, and that everything else is formed from it by its condensation and rarefaction and change of qualities. That is what Theophrastus records about Diogenes, and the book of his which has survived up to my time, On Nature, clearly states that air is that from which everything else comes into existence. (Theophrastus [fr. 226a Fortenbaugh et al.] in Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 25.1–8 Diels)
F1 (DK 64B1; KRS 596) This is how Diogenes starts his book: ‘It is my opinion that at the start of any book a writer ought to make his starting-point indisputable, and his methodology straightforward and authoritative.’* (Diogenes Laertius, Lives of Eminent Philosophers 9.57.12–14 Long)
F2 (DK 64B2; KRS 599) In brief, then, it is my opinion that all existent things are modifications of the same thing and are the same thing. This is transparently obvious: if the things that exist in this universe—earth, water, air, fire and all the other things which plainly exist in this universe—if any of them was different, essentially different, from anything else, rather than being the same but changing and modifying in a number of ways, it would be completely impossible for things to mix with one another, or for one thing to help or harm another, or for a plant to grow from the earth or for a living creature or anything else to come into existence, unless they were all the same thing in terms of their composition. No, all these things are modifications of the same thing: they become differently qualified at different times and return back to the same thing. (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 151.31–152.7 Diels)
F3 (DK 64B3; KRS 601) Without intelligence it is inconceivable that matters would be disposed in such a way as to contain measures of everything—of winter and summer, night and day, rain and warmth,† wind and sunshine. And anyone who cares to think about it will find that everything else too is in the best possible condition.* (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 152.12–16 Diels)
F4 (DK 64B4; KRS 602) Moreover, here is powerful evidence in support of what I have been saying: human beings and all other living creatures are alive because of air, since they breathe. Air is for them both soul and intelligence, as will be explained in this book of mine, and in the absence of air they die and their intelligence fails. (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 152.18–21 Diels)
F5 (DK 64B5; KRS 603) It is also my opinion that the possessor of intelligence is what men call air, and that everything is steered and controlled by air. I say this because it is my opinion that air is a god, and pervades everything, manages everything, and is present in everything. There is nothing that does not partake of air. However, there is nothing that partakes of air in the same way as anything else; there are many modes not only of air itself, but also of intelligence. For the modes of air are diverse: it may be warmer or cooler, drier or wetter, more or less mobile, and it contains the possibility of many, infinitely many, modifications in terms of taste and colour. In all living creatures soul is the same—air that is warmer than the outside air in which we live, but much cooler than the air near the sun—but in no two living creatures is this warmth identical. After all, even human beings differ from one another in this respect. The difference between creatures is not great, however, but small enough to allow them to be similar. It is impossible, though, for any of the things that undergo modification to become absolutely identical to anything else without actually being the same thing. In so far, then, as modification is diverse, living creatures are diverse too, and there is a plurality of them, with the diversity of modifications responsible for their dissimilar characteristics, ways of life, and kinds of intelligence. Nevertheless, it is by means of the same one thing that all living creatures live and see and hear, and the rest of their intelligence too stems from the same one thing. (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 152.22–153.13 Diels)
F6 (DK 64B7; KRS 604) Although this very thing is an eternal and immortal body, it is thanks to this body† that some things come into existence and others depart. (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 153.19–20 Diels)
F7 (DK 64B8; KRS 605) But it seems clear to me that it is great, powerful, eternal, immortal, and possessed of wide knowledge. (Simplicius, Commentary on Aristotle’s ‘Physics’, CAG IX, 153.20–2 Diels)
T2 (DK 64A6; KRS 607) Diogenes of Apollonia supposes that air is the elemental stuff, that everything is in motion, and that there is an infinite number of worlds. His cosmogony is as follows: the universe was in motion and became rare in some places and dense in others; where a dense part coincided with rotational movement it created the earth, and all the other worlds were formed in the same way; but the lightest parts took the upper level and formed the sun. (Ps.-Plutarch, Miscellanies 12 Diels)
T3 (DK 64A12; KRS 608) Diogenes says that the heavenly bodies are pumice-like, and he thinks of them as the breathing-holes of the universe.* The heavenly bodies are fiery, he says. Along with the visible bodies are carried around invisible stones which, being invisible, have gone unrecognized. They often fall to the earth and are extinguished, as happened to the rocky heavenly body that fell in a blaze of fire at Aegospotami. (Aëtius, Opinions 2.13.5 Diels)
T4 (DK 64A13) Diogenes says that the sun is pumice-like, and that its beams are fixed into it from the aither. (Aëtius, Opinions 2.20.10 Diels)
T5 (DK 64A13) Diogenes says that the sun is extinguished by cold which counteracts its warmth. (Aëtius, Opinions 2.23.4 Diels)
T6 (DK 64A16) Diogenes says that fire impacts on moist cloud, and causes thunder by being extinguished and lightning by its brilliance; he also attributes these phenomena to wind. (Aëtius, Opinions 3.3.8 Diels)
T7 (DK 64A19; KRS 612) Diogenes relates sense-perception to air, just as he does life and intelligence. Apparently, then, he attributes perception to similarity, because he says that there would be no action or being acted upon unless everything came from a single thing.*
He says that smell is caused by the air around the brain, there being an accumulation of air there which is commensurate with an odour, since the brain itself is open-textured because of its veins.† But then there are those creatures in whom the condition of the air is not commensurate and fails to mingle with odours—their brains are extremely fine. Obviously, then, perception occurs when there is commensurability with the blending.* Hearing occurs when the air inside the ears is set in motion by the air outside and passes through to the brain. Sight occurs when things are reflected on the pupil, and the pupil, by mixing with the air inside, produces perception. This is proved by the fact that if the veins become inflamed, there is no mixture with what is inside and seeing does not occur, even though the reflection is present just as much as before.* Taste occurs in the tongue, he says, because it is open-textured and soft. He completely fails to explain how touch occurs or what its proper objects are.
Next he tries to describe what is responsible for keener senses and what kinds of creatures have keener senses. Smell is keenest in those who have the least air in their heads, because then the mingling can take place most rapidly. Also, the longer and narrower the channel through which the air is drawn in, the better, because this enables the odour to be detected more quickly. That is why some creatures have a better sense of smell than humans do. All the same, if the odour were composed commensurately with the air in a man’s brain, his sense of smell would be excellent.
Those creatures have the sharpest hearing whose veins are fine, and in whom the passages which are as relevant to hearing as to smell are short and fine and straight, and also in whom the ears are upright and large, because it is when the air in the ears moves that it sets in motion the air inside. But if the ears are rather wide, when the air in the ears moves there is an echo and an indistinct noise because the air inside which it meets is not still.
Those creatures see best whose inner air and veins are fine (which is also the case for the other senses too), and whose eyes are brightest. Opposite colours are reflected best, and so dark-eyed people see better in the daytime and see bright objects better, while people with the opposite kinds of eyes see better at night.
That it is the inner air that perceives, as being a fragment of the god, is shown by the fact that often when our minds are preoccupied with other matters we fail to see or hear.
Pleasure and pain occur as follows. When a lot of air mingles with the blood and makes it light, which is a natural occurrence, and pervades the whole body, pleasure is the result. When the unnatural happens and the air does not mingle, the blood gets heavier and weaker and thicker, and pain is the result. The same goes for confidence and health and their opposites. The tongue is what discerns pleasure most,* because it is particularly soft and fine and all the veins are connected to it. That is why so many symptoms of illness can be found on the tongue, and in other creatures their colours are revealed by the tongue; for the variety and quality of these colours are reflected on their tongues. Anyway, so much of how and under what circumstances perception occurs.
As for thinking, as I have already said, Diogenes attributes it to pure, dry air, since moisture impedes the mind. That is why thinking is impaired in people who are asleep or drunk or overfull. That moisture is detrimental to the mind is proved by the inferior intelligence of creatures other than man, which is due to the fact that the air they breathe arises from the earth and that the food they eat has a higher moisture content. As for birds, although they breathe pure air, in their constitution they resemble fish, in the sense that their flesh is firm and the air they breathe does not pervade the whole body, but halts in the region of the belly. That is why, although they digest food quickly, they remain stupid in themselves. Their mouths and their tongues also have a part to play in their stupidity, as well as their food, because they cannot understand one another. Plants have no intelligence at all, because they have no hollows and take in air.
This also explains why children lack intelligence: they have a great deal of moisture in their bodies, with the result that the air cannot penetrate deep inside their bodies, but gets no further than their chests before being excreted. That is why they are slow and stupid. They are liable to tantrums, and are emotionally unstable and fickle because a lot of air is excreted out of their small bodies. This is also why a child is forgetful, because the failure of the air to pervade the whole of its body means that it is incapable of comprehension. Proof of this is that when we try to remember something we feel a blockage in the chest, and when we remember it, the blockage clears and the pain is relieved. (Theophrastus, On the Senses 39–45 Stratton)
F8 (DK 64B6; KRS 615) Here is what the veins in man are like. There are two particularly large ones which extend through the belly along the spine, one to the right of the spine and one to the left; each of these goes down to the leg on its side of the body and up to the head, going past the collar-bones and through the throat. Further veins spread from these two all through the body, those on the right of the body stemming from the one on the right, and those on the left from the one on the left. The largest of these secondary veins are two which enter the heart in the region of the spine, and two others a little higher up which run through the chest, under the armpits and down to the hands, each to the hand that is on its side of the body. One of these is called the spleen-vein, the other the liver-vein. Each of them divides into two at the end, with one branch going down to the thumb, and the other to the palm of the hand, and a number of fine, many-branched cuts stem off from these to the rest of the hand and the fingers. Other, even finer veins run from the primary veins, the ones on the right to the liver, and the ones on the left to the spleen and the kidneys. Those which run down into the legs divide at the groin and then run down the whole thigh. The largest of these runs down the back of the thigh and is readily visible as a thick vein, while the other, which runs down the inside of the thigh, is a little less thick. Then they extend past the knee to the shin and the foot, just like the ones which go down into the hands. They extend down to the sole of the foot and then their branches run to the toes. There are also a large number of fine veins which split off from these veins and run towards the belly and the flanks.
The veins which run into the head through the throat can be seen to be large in the neck. Each of them, at its end, divides into many veins which extend into the head, some passing from the left to the right and others from the right to the left. They end by the ears on either side. There is another vein in the neck, which runs alongside the large ones on either side. They are a little smaller than the large ones, to which the majority of the veins from the head are connected. They too run through the throat, but on the inside of the throat, and from each of them others run under the shoulder-blades and down into the arms, and are visible alongside the spleen-vein and the liver-vein, a little smaller in size; these are the veins doctors lance† to treat subcutaneous pain. For pain in the region of the belly, however, they lance the liver-vein and the spleen-vein. Other veins branch off from these and run under the breasts.
There are other fine veins which run on either side of the body through the spinal marrow and into the testicles; another pair runs through the flesh, under the skin, to the kidneys, and end in men in the testicles and in women in the uterus. These veins are called the spermatic veins.† The veins which run from the belly are at first fairly wide, but then they become finer, until they change over from the right to the left and from the left to the right. The thickest part of the blood is absorbed by the fleshy parts of the body, while the excess, which runs into the parts I have been talking about, becomes fine and warm and frothy. (Aristotle, Enquiry into Animals 511b31–512b11 Bekker)
J. R. Shaw, ‘A Note on the Anatomical and Philosophical Claims of Diogenes of Apollonia’, Apeiron, 11.1 (1977), 53–7.