On the Motion and Gait of Animals

Summary

This record joins two brief Aristotelian treatises that ask how a living thing gets from one place to another. The Motion of Animals (De Motu Animalium, eleven short chapters) asks what all animal movement has in common; the Gait of Animals (De Incessu Animalium, nineteen chapters, often called the Progression of Animals) asks why particular animals have the limbs they have and bend them as they do. Read together they move from cosmology to the knee joint and back again. The Motion of Animals opens with a mechanical principle: nothing that moves itself can do so unless something is at rest. A bent elbow pivots on a point that stays still while the forearm swings; a walker needs ground that does not give way, as mice slip in heaped grain and men in sand; a man inside a boat cannot pole it forward by pushing against the boat itself. Aristotle then widens the principle to the heavens, criticising the myth of Atlas and those who make the poles a source of motion, and quoting Homer's Zeus, whom no god can drag down by a golden chain, to argue that the first mover of the universe must lie outside what it moves. The centre of the treatise is psychological. Chapter 6 names the movers of an animal as intellect, imagination, purpose, wish and appetite, and reduces them to thought and desire; the object desired, a real or apparent good, moves without being moved, as the prime mover does. Chapter 7 then gives Aristotle's best-known account of what later readers call the practical syllogism: two premises, one about the good and one about the possible, issue not in a proposition but in an action. "I need a covering, a coat is a covering": the man makes a coat. Aristotle compares the body to automatic puppets and a child's toy cart, but notes that living parts also swell and shrink with heat and cold, so that a mere image can make us shudder or blush. Chapters 9-11 locate the soul's moving origin in the middle of the body, near the heart, name the connate spirit (pneuma) as its instrument, liken the well-ordered body to a city that needs no magistrate at every post, and separate voluntary movement from involuntary movements of the heart and genitals and non-voluntary ones such as sleep and breathing. The Gait of Animals turns comparative. Starting from the rule that nature does nothing in vain, Aristotle defines the body's six directions, explains why blooded animals move at no more than four points, why snakes have no legs, why man alone stands upright, why birds have two legs and wings rather than four legs, and why men and quadrupeds bend their limbs in opposite directions. The treatise is an early attempt to explain anatomy by function.

Plot or Argument

• The point at rest (Motion of Animals 1-4)

  Every self-mover needs a fixed point within (the joint) and a resisting support without (ground, air, water). The boat that cannot be poled from inside and the Atlas myth extend the rule to the cosmos: the first mover of the heavens must be outside and unmoved.

• Growth and generation set aside (ch. 5)

  A short chapter notes that the same question can be asked of growth and alteration, but that nothing can be the cause of its own generation, since the begetter must exist before the begotten.

• Thought and desire as movers (ch. 6-8)

  Intellect, imagination, purpose, wish and appetite reduce to mind and desire. The object of desire is a practical good, real or seeming. Premises of the good and the possible conclude in action; images and memories alter the body's heat and so set the limbs going, like a rudder moved a hair's breadth.

• The central seat and the connate spirit (ch. 8-10)

  The arm-and-stick argument shows the true origin of movement cannot lie in any limb; it must be central, in or near the heart. Connate pneuma, able to expand and contract, pushes and pulls. The organism is compared to a well-governed commonwealth.

• Involuntary and non-voluntary motions (ch. 11)

  The heart and the generative organ move at an image without reason's command; sleep, waking and breathing are non-voluntary. The treatise closes by announcing that animal generation remains to be treated.

• Principles of locomotion (Gait of Animals 1-6)

  Nature does the best possible for each kind; animals have six directional boundaries (above-below, front-back, right-left); movement begins from the right; thrust and pull are the origins of change of place.

• Feet, numbers and flexion (Gait 7-14)

  Blooded animals move at no more than four points, so long-bodied snakes are limbless; man alone is erect; human arms and legs bend in opposite senses, quadrupeds cross their gait (off fore, near hind, near fore, off hind).

• Birds, crabs, fish and molluscs (Gait 15-19)

  Wings stand in for forelegs; crabs walk sideways because their side does the work of a front; fins answer to wings and legs; molluscs and seals are treated as creatures whose motion is imperfect or misshapen.

Characters

• Homer, poet cited

  Aristotle quotes the Iliad passage in which Zeus defies the gods to drag him from heaven by a chain, as poetic support for an unmoved first mover.

• Atlas (in the mythologists' account), foil

  The giant who turns the heavens with his feet on the earth; Aristotle treats the myth as intelligent but shows that it makes the earth's resistance equal to the force of the whole heavens.

• The automaton and the toy cart, governing analogy

  Puppets set going by released levers and twisted cords, and a child's wagon with unequal wheels, model how a small initial change produces large movement, while differing from animals in lacking qualitative change.

Lessons

• Every push needs a place to stand

  Aristotle's first claim is physical and easily tested: a joint moves only because one point in it is still, and an animal advances only by pressing on something that resists. The sand, the heaped grain and the boat give students experiments they can perform. The principle then grounds his argument that the universe itself depends on a mover outside it.

  • Why can a man move a boat by poling from the bank but not by pushing on the mast while standing in it?
  • Aristotle moves from the elbow to the heavens. Is the step from a joint to the whole cosmos a fair inference or only an analogy?
  • What modern devices (a rowing oar, a rocket) seem to test his principle, and how would he answer them?

• The coat syllogism: how a reason becomes a deed

  In chapter 7 Aristotle says that practical reasoning concludes not in a statement but in an action: I need a covering, a coat is a covering, so I make a coat. He adds that we often skip the obvious premise, and that appetite can supply the conclusion at once (I want to drink; this is drink). This passage is a starting point for his ethics of deliberation and for many later accounts of moral action.

  • What two kinds of premise does Aristotle say every action requires, and why must both be present?
  • If the conclusion is an action, what has happened when someone reasons correctly but does not act?
  • How does 'a seeming good may take the room of actual good' help explain a bad choice?

• An image can move the body

  Aristotle notes that imagined objects affect the body as real ones do: we shudder at a mere idea, blush and turn pale, and memories and anticipations bring the same changes of heat. A tiny change at the centre, like a rudder moved a hair's breadth, makes a large change at the periphery. The passage invites careful attention to what we allow ourselves to imagine and dwell on, a theme Christian moral teachers also took up when they spoke of guarding the heart and the thoughts.

  • What examples does Aristotle give of the body responding to things only imagined or remembered?
  • Why does he think the small change must happen near the heart rather than in the limbs?
  • Does his account support the old counsel that disciplining the imagination is part of disciplining the will?

• The body as a well-governed city

  At the end of chapter 10 Aristotle compares the organism to a commonwealth where, once order is established, no separate ruler is needed at each task; the soul resides centrally and the parts do their work by natural structure. The image describes a hierarchy in which order is distributed rather than micromanaged. Students can test it against what he says about involuntary movements, which happen without the ruler's command.

  • What does the political image explain about the body that the puppet image does not?
  • How do the heart's and generative organ's involuntary movements complicate the picture of a well-ordered city?
  • Where else in Aristotle (for instance in the Politics or the Ethics) does the relation of rule between soul and body appear?

• Nature makes nothing in vain: reading the limbs

  The Gait of Animals assumes that each anatomical feature is the best possible for the animal's kind and then asks why: why snakes are limbless, why man alone stands erect with legs heavier than his upper body, why children cannot walk upright at first, why human limbs bend in opposite directions. Some of his answers are wrong, but the method of asking what a structure is for proved durable in later anatomy.

  • What reason does Aristotle give for snakes having no legs, and is it a good explanation?
  • How does he use the proportions of small children as evidence about upright walking?
  • Can one keep his question 'what is this part for?' while rejecting some of his particular answers?

Context

Both treatises belong to the Aristotelian corpus of works on living things, alongside the History of Animals, Parts of Animals, Generation of Animals, De Anima and the short Parva Naturalia. The Motion of Animals draws together physics, psychology and cosmology: its opening cross-references point to the Physics and to the Metaphysics on the eternal mover, and its closing sentence lists the treatises on parts, soul, sense-perception, sleep and memory as finished, leaving generation. The Gait of Animals is narrower, a functional comparison of locomotive organs that assumes the observational data of the History of Animals.

Composition

Neither treatise can be dated precisely. The Motion of Animals refers back to the investigation of animal movements 'after their various kinds', usually taken to be the Gait of Animals, and to De Anima, so it is generally placed late among the biological works, probably in Aristotle's second Athenian period (335-322 BC). Its authenticity was questioned by some nineteenth-century scholars; Werner Jaeger defended it in 1913, and Martha Nussbaum's 1978 edition and commentary reflects the now usual acceptance. The library's text is the Oxford translation by A. S. L. Farquharson (1912).

Reception

Both works circulated in Greek commentary and were translated into Latin in the Middle Ages as part of the natural books studied in the universities. The practical-syllogism passage of the Motion of Animals became a reference point for medieval and modern accounts of action. In the seventeenth century Giovanni Alfonso Borelli gave the title De Motu Animalium (1680-81) to his mechanical study of muscles and joints, a sign of how the question Aristotle framed was taken up with new tools. Modern philosophers of action and historians of biology read the treatises as early attempts to join psychology and physiology. The work was chosen for the Great Books of the Western World (2nd ed., 1990), volume 8.

Comparisons

• De Anima

  De Anima III.9-11 asks what in the soul moves the animal and answers with desire and its object; the Motion of Animals cites that discussion and adds the bodily mechanism, the central seat and the connate spirit, that De Anima leaves out.

• The Nicomachean Ethics

  The coat-and-covering reasoning of Motion of Animals 7 is the physiological counterpart of deliberation and choice in Ethics III and of the account of incontinence in Ethics VII, where a man may hold the right premise and still act on appetite.

• Metaphysics

  Metaphysics XII describes a first mover that moves as an object of love and desire; Motion of Animals 6 explicitly parallels the animal's movement by its desired good with the heaven's movement by the eternal good.

• Parts of Animals

  Parts of Animals explains organs by their function in general; the Gait of Animals applies the same 'nature does nothing in vain' reasoning narrowly to legs, wings, fins and the direction of flexion.

• On the Motion of the Heart and Blood in Animals (De Motu Cordis)

  Aristotle makes the heart the seat of the moving soul and of sensation; Harvey, who admired Aristotle, kept the heart's primacy but described its motion as a muscular pump driving the circulation, replacing the connate spirit with measured anatomy.

• Discourse on Method

  Aristotle compares animals to automatic puppets but insists that living parts change in quality under images and desires; in Part V of the Discourse Descartes went further, treating animal bodies as machines and sharpening the question of how a rational soul moves a human body.

Quotes

Medical Lens

The Motion of Animals is one of the earliest sustained attempts to say how a mental event becomes a bodily movement. Aristotle's chain runs from perception or imagination, through desire, to a change of heat at the heart, carried by the connate spirit (pneuma) to the limbs. He uses this to explain why imagined or remembered objects produce shuddering, blushing, pallor and goose-flesh, and why the heart and the genitals move at an image without the command of reason. He also distinguishes non-voluntary bodily processes such as sleep, waking and respiration. The cardiocentric physiology and the doctrine of connate pneuma were later disputed by Galen and the Alexandrian anatomists, who placed the ruling part in the brain and nerves. Readers should treat these passages as the history of physiological psychology, not as clinical description; any link to modern psychosomatic medicine is an interpretive comparison.

• Motion of Animals, ch. 7

  Images and conceptions alter bodily heat as real objects would; a slight change in the region of the heart produces blushing, pallor, shivering and goose-flesh at the periphery.

  Mind Body
• Motion of Animals, ch. 8

  Pleasure and pain, courage, panic and erotic feeling are each accompanied by a change of temperature; memories and anticipations cause the same changes in weaker form.

  Mind Body Ancient Medicine
• Motion of Animals, ch. 10

  Connate spirit, seated in or near the heart, expands and contracts to push and pull, serving as the material instrument of the soul's movement.

  Ancient Medicine
• Motion of Animals, ch. 11

  Involuntary movements of the heart and generative organ at an image, and non-voluntary processes such as sleep, waking and breathing, explained by natural changes of temperature.

  Mind Body Sleep Insomnia

Creative Prompts

• Classroom

  Test the first chapter: try to move a rolling chair while sitting in it and pushing only on the chair, then by pushing on the floor. Write up the result in Aristotle's terms of the point at rest and the external support.

• Essay

  Write an essay on the coat syllogism of chapter 7. Explain how premises about the good and the possible issue in an action, then use the Nicomachean Ethics to discuss what goes wrong when a person knows the right premise and does not act.

• Dialogue

  Write a dialogue between Aristotle and Harvey over a dissected heart: one defends the heart as seat of the moving soul and connate spirit, the other describes the pump and the circulation.

• Classroom

  Watch a dog, cat or horse walk slowly and record the order in which its feet leave the ground. Compare your record with the crossed gait described in Gait of Animals, ch. 14.

Further Reading

• Aristotle's De Motu Animalium: Text with Translation, Commentary, and Interpretive Essays, Martha C. Nussbaum

  The standard English edition and commentary (Princeton, 1978), including essays on the practical syllogism and on teleological explanation.

• Aristotle's Philosophy of Biology, James G. Lennox

  Essays on Aristotle's biological method and teleology.

• De Anima, Aristotle

  Book III.9-11 on the soul's power to move the animal.

• On the Motion of the Heart and Blood in Animals, William Harvey

  The 1628 treatise that kept the heart's primacy while overturning much of the older physiology.