Instructor's Notes: Aristotle's Physics, Book II

1. Socrates had inquired about the nature of things, such as piety, and Plato had claimed that the nature of things is their form. A form says what a thing is. Plato's theory of forms was quite limited in one sense: that it had little to say about why things come to be what they are not originally.

Aristotle defines the nature of a thing as a principle of change (motion and rest) which is based on what a thing is. He claimed that it is self-evident that there are natures. The attributes or properties of a thing depend on them.

Previously to Aristotle, there were two rival theories of what natures are:

  1. the primary underlying matter of which a thing is made (materialist)
  2. the shape or form specified in the definition of the thing (formalist or Platonist)
Aristotle agreed with Plato and against the materialists that the form is the nature, for two reasons:

  1. The form is what a thing is (a bed) and matter only the potential (wood), but the nature pertains to the actual
  2. The form is the end of the process of coming to be (a bed), while matter is that which comes to have the form (the wood); and the nature pertains to the result.

2. The object of sciences of nature is the form which is separable from the matter in thought but not in existence. Once again, Aristotle diverges from Plato's theory of forms, according to which forms are intelligible objects existing in their own right, more real than the things which have them. But he also disagrees with the materialists known as atomists.

3. We don't know a thing until we grasp the why of it "which is to grasp its primary cause." This holds for coming to be and passing away. Here Aristotle enunciates the famous doctrine of the "four causes," which are:

  1. That out of which a thing comes to be and which presists (bronze, metal)
  2. Form or archetype (2:1 ratio, number)
  3. Primary source of change or rest (father)
  4. The end or that for the sake of which (health).
There are several causes of the same thing (art of the sculptor and bronze are causes of the statue insofar as it is a statue, as opposed to just a piece of bronze). Some cause are reciprocal, in the sense that x causes y and y causes x. Hard work causes fitness, since it is the source of change, but fitness causes hard work, in that it is the end to which hard work is directed. Similarly, the letters are material whose form is the material.

Aristotle then uses this classification of causes to make a number of other distinctions which will not be discussed here.

4. No discussion of change and its causes can escape the question of whether they can occur hy chance. Some say nothing happens by chance, "chance" events can be explained otherwise. The dice came up "snake eyes" when I rolled them because of complex physical interactions between them, my hands and the table. Others say that there are spontaneous acts, not based on causes. For example, some atomists thought that the present order of things is the result of a random swerve in an atom, which then set off a chain reaction of motions among the atoms. This is a surprising result, according to Aristotle, because at the same time they think that all inteactions among organized bodies (animals, for example) are based on causes.

5. Aristotle asserts an important principle that philosophers have argued about ever since: that chance cannot be the cause of what happens always or for the most part the same way.

Things which happen for the sake of something (intention or nature) are said to be by chance when they come to be accidentally. One goes for some purpose to a place and accidentally finds he can raise funds for a banquet there. It would not be by chance if he went by necessity, always went, or went to raise the subscription.

Note: the following sections are not in completed form.

6. Chance and spontaneity differ in that spontaneity is wider. "Chance and what results form chance are appropriate to agents that are capable of good fortune and of action generally." This rules out an inanimate thing, beast or child as subject to chance. But they can do things spontaneously, since they still do things for the sake of something in the broad sense. Chance and spontaneity both belong to "the source of change." There is an actual agent but there is an infinity of possible agents.

7. The student of nature will assign the "why" in a way proper to his science. The form, mover and end "often coincide, for the what and that for the sake of which are one, while the primary source of motion is the same in species as these ."

We usually ask for the "primary moving cause" in cases of coming to be: "'what comes to be after what? what was the primariy agent or patient?' and so at each step of the series."

The form causes motion but is not moved.

8. Why does nature act for the sake of something? Necessity must also be explained. Why do things not happen just from necessity? The rain did not fall to water my crops or to spoil the grain on the threshing-room floor.

But this cannot be right. The result of chance or spontaneity are not (by definition) things that happen always or for the most part.

The relation between earlier and later is the same in nature as in art [precursor of the design argument].

This is most clear in non-human animals. They do not proceed by intelligence, though for an end. The same with plants. The form is what constitutes the end, and "the form must be the cause in the sense of that for the sake of which."

Mistakes are possible in the operations of nature as well as those of man. So mistakes indicate corruption of a principle.

Nature is like a doctor doctering himself. It is a cause, operating for a purpose.

9. What is necessary is necessary on a hypothesis, not as an end. The physical properties of the components of a house are necessary for the house but not its end. "The wall does not come to be without these, itis not due to these, except as its material cause; it comes to be for the sake of sheltering and guarding certain things."

The necessary is matter and the changes in it.

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