On Generation and Corruption

Summary

On Generation and Corruption (Greek Peri Geneseos kai Phthoras; Joachim translates the title On Coming-to-be and Passing-away) is Aristotle's two-book inquiry into the most basic kinds of natural change below the moon. It asks what happens when a new substance comes into existence or an old one is destroyed, how that differs from a thing merely changing its qualities or its size, what contact, action and mixture are, and how the four simple bodies, earth, water, air and fire, turn into one another. It sits between the Physics, which treats motion in general, and the Meteorology and biological works, which treat compounds and living things. Book I begins with a survey of predecessors. Aristotle sets the monists, who reduce all change to alteration of one stuff, against the pluralists Empedocles, Anaxagoras, Leucippus and Democritus, who treat coming-to-be as the gathering and scattering of permanent elements. He reserves real praise for Democritus, who alone argued 'from the science of nature' rather than dialectically, and then refutes the atomists' indivisible bodies. Against them he argues that there is unqualified coming-to-be, the generation of a substance from what is not yet that substance, and that it can go on forever because one thing's passing-away is another's coming-to-be. He distinguishes alteration, in which a perceptible subject persists while its qualities change (a body now healthy, now ill), from generation, in which nothing perceptible persists. He explains growth as food, potentially flesh, being converted into the form of flesh. He then analyses contact, acting and being acted upon, rejects Empedocles' pores and the void, and defines mixture: when two bodies of balanced power act on each other, a genuinely new uniform stuff results, whereas a drop of wine in ten thousand gallons of water simply vanishes into the water. Book II turns to the elements. The primary tangible contraries are hot and cold, dry and moist; their four possible pairings give fire (hot and dry), air (hot and moist), water (cold and moist) and earth (cold and dry). Because each shares a quality with its neighbours, every element can become every other, most easily those that differ by one quality, so the elements change in a cycle. Every compound contains all four. Aristotle then names the causes of coming-to-be: matter, form, and an efficient cause, which neither Plato's Forms in the Phaedo nor mere matter supply. That cause is the sun's yearly motion along the inclined circle of the ecliptic, generating as it approaches and destroying as it withdraws. In the closing chapters he argues that because being is better than not-being, and perishable things cannot be eternal individually, the continual recurrence of generation is the nearest approach to eternity, and that only cyclical sequences, such as rain and cloud, are absolutely necessary.

Top Lessons

• Changing versus becoming something new

  Aristotle's key distinction is between alteration, where the same perceptible subject persists with new qualities, and generation, where one substance perishes and another arises. A sick body that recovers is the same body; water that becomes air is no longer water. The distinction asks students to say precisely what remains through a change, a habit useful in chemistry, biology and theology alike.

• Experience before system

  In I.2 Aristotle says that lack of experience narrows our view of the facts, and that those who live close to nature form better principles than those who dogmatize from a few observations. He uses this to prefer Democritus's physical arguments to the Platonists' geometrical ones, even while rejecting Democritus's conclusion. The passage is an ancient statement of the duty to look before theorizing.

• The drop of wine in the sea

  Aristotle's theory of mixture holds that a true compound arises only when ingredients of comparable power act on one another and both change into something new. If one is overwhelmingly greater, the lesser is simply converted into it, as a drop of wine disappears into ten thousand gallons of water. Students can compare this with modern distinctions between mixtures, solutions and compounds, and notice what questions survive the change of theory.

• The sun's inclined path as cause of birth and decay

  Aristotle argues that a single uniform motion would cause only one kind of effect; generation and destruction need a motion that approaches and retreats. The sun on the ecliptic does this, so things come to be as it nears and decay as it withdraws, and each kind of living thing has a life measured by a period. The argument links the seasons, agriculture and mortality in one causal picture.

• Perpetual generation as a likeness of eternity

  In II.10 Aristotle says nature strives after the better, and since perishable things cannot possess being forever, God completed the universe by making coming-to-be continuous, the closest approximation to eternal being. The cycle of the elements imitates the circular motion of the heavens. This is Aristotle's god, a first principle of an eternal cosmos, not the Creator of Genesis; Christian readers such as Aquinas used his physics while rejecting the eternity of the world on the ground of revelation.

Verified Quotes

Medical Lens

This is a work of physics, not medicine, but it supplies the theory of four primary qualities (hot, cold, dry, moist) that Greek and later Galenic physicians used to describe bodies, foods and drugs. Its account of growth explains nutrition as food that is potentially flesh being converted into actual flesh, and it repeatedly uses the physician and the art of healing as its model of an agent that acts without being acted upon. The treatise does not discuss the four humours themselves; any link to humoral pathology runs through later writers rather than through this text.

• Book I, ch. 5

  Growth explained as food, potentially flesh, being converted into the form of flesh; the same food nourishes and causes growth in different respects.

• Book I, ch. 7

  The art of healing produces health without being acted on by the patient, while food acts and is acted on; used to distinguish first agents from last ones.

• Book II, ch. 2-3

  Hot, cold, dry and moist set out as the primary tangible contraries and paired to form the four simple bodies, the qualitative scheme later used in Greek medical theory.