Aristotle's Physics: Motion, Causation, and Change

For the Greek philosophers, the problem of physis is closely linked to movement. Aristotle is the first to make a systematic presentation on the problem of motion. He formulates in a clear way that mobility is the basic mode of reality. Nature is to say that natural things are in motion. To define physis, Aristotle distinguishes between natural beings (from the physis) and artificial things (which come from other causes). Natural beings have movement within themselves; every body has a natural place, and motion is identified with change (any type of change is movement, according to Aristotle).

Aristotle's physics begins with a critique of Parmenides, who stated that motion is irrational. Aristotle introduces two new concepts: there are two ways of being: not-being absolute and not-being relative. Something that is not absolutely is what is not and cannot be. Something that is not something relative is not, but it can be. What is not but can be is found in potency over what can be. (Example: the seed is not a tree, but may become one; therefore, it is a tree in potency). Being in potency is the ability to become something that is not yet. However, things are in the act of what they are. At that time, movement is defined as the renovation of a being in power in what is in potency; that is, the passage from potency to act.

Theory of Causation

Aristotle's theory of causation explains the types of change:

The cause of each thing is its nature. Types of causation:

• Intrinsic Causes:
  • Material Cause: The material of which a thing is made.
  • Formal Cause: The form, the essence that makes something what it is.
• Extrinsic Causes:
  • Efficient Cause (or Moving Cause): What makes the thing, what produces something.
  • Final Cause: The purpose for which a thing is made, what something is used for.

In all natural things, the efficient cause, the formal cause, and the final cause coincide.

Types of Change

Changes are relevant to the substance (ousia) or accidents:

• Substantial Change: Generation of a new substance or the destruction of an existing one.
• Accidental Change: Modification of an accident of the substance. Depending on the accident that is affected, it may be:
  • Change in quantity (increase or decrease)
  • Change in quality (alteration)
  • Change in location (translation)

Change: Conversion of what is in potency to the act, or the process by which a substance acquires a form it lacked, or the materialization of form.

Movement: The act of what is potential insofar as it is in potency.