Potentiality and Actuality - Motion

Motion

Aristotle discusses motion (kinēsis) in his Physics quite differently than modern science does. Aristotle's definition of motion is closely connected to his actuality-potentiality distinction. Taken literally, Aristotle defines motion as the actuality (entelecheia) of a "potentiality as such". What Aristotle meant however is the subject of several different interpretations. A major difficulty comes from the fact that the terms actuality and potentiality, linked in this definition, are normally understood within Aristotle as opposed to each other. On the other hand the "as such" is important and is explained at length by Aristotle, giving examples of "potentiality as such". For example the motion of building is the energeia of the dunamis of the building materials as building materials as opposed to anything else they might become, and this potential in the unbuilt materials is referred to be Aristotle as "the buildable". So the motion of building is the actualization of "the buildable" and not the actualization of a house as such, nor the actualization of any other possibility which the building materials might have had.

Sachs (2005) and Coope (2009) both list three major interpretations. The following is based on the discussion of Sachs:

1. The interpretation of Averroes, Maimonides, and W.D. Ross.

This interpretation is, to use the words of Ross that "it is the passage to actuality that is kinesis” as opposed to any potentiality being an actuality.

The argument of Ross for this interpretation requires him to assert that Aristotle actually used his own word entelecheia wrongly, or inconsistently, only within his definition, making it mean "actualization", which is in conflict with Aristotle's normal use of words. According to Sachs (2005) this explanation also can not account for the "as such" in Aristotle's definition.

Kosman (1999) published a similar criticism of Ross, that was originally printed in 1969.

2. The interpretation of St Thomas of Aquinas.

Sachs (2005) explains that in this explanation "the apparent contradiction between potentiality and actuality in Aristotle’s definition of motion" is resolved "by arguing that in every motion actuality and potentiality are mixed or blended". Motion is therefore "the actuality of any potentiality insofar as it is still a potentiality". Or in other words:

The Thomistic blend of actuality and potentiality has the characteristic that, to the extent that it is actual it is not potential and to the extent that it is potential it is not actual; the hotter the water is, the less is it potentially hot, and the cooler it is, the less is it actually, the more potentially, hot.

As with the first interpretation however, Sachs (2005) objects that:

One implication of this interpretation is that whatever happens to be the case right now is an entelechia, as though something that is intrinsically unstable as the instantaneous position of an arrow in flight deserved to be described by the word that everywhere else Aristotle reserves for complex organized states that persist, that hold out against internal and external causes that try to destroy them.

3. The interpretation of Sachs.

Sachs (2005), amongst other authors (such as Kosman and Coope), proposes that the solution to problems interpreting Aristotle's definition must be found in the distinction Aristotle makes between two different types of potentiality, with only one of those corresponding to the "potentiality as such" appearing in the definition of motion. He writes:

The man with sight, but with his eyes closed, differs from the blind man, although neither is seeing. The first man has the capacity to see, which the second man lacks. There are then potentialities as well as actualities in the world. But when the first man opens his eyes, has he lost the capacity to see? Obviously not; while he is seeing, his capacity to see is no longer merely a potentiality, but is a potentiality which has been put to work. The potentiality to see exists sometimes as active or at-work, and sometimes as inactive or latent.

Coming to motion, Sachs gives the example of a man walking across the room and says that...

• "Once he has reached the other side of the room, his potentiality to be there has been actualized in Ross’ sense of the term". This is a type of energeia. However it is not a motion, and not relevant to the definition of motion.
• While a man is walking his potentiality to be on the other side of the room is actual just as a potentiality, or in other words the potential as such is an actuality. "The actuality of the potentiality to be on the other side of the room, as just that potentiality, is neither more nor less than the walking across the room."

Sachs (1995, pp. 78–79), in his commentary of Aristotle's Physics book III gives the following results from his understanding of Aristotle's definition of motion:

The genus of which motion is a species is being-at-work-staying-itself (entelecheia), of which the only other species is thinghood. The being-at-work-staying-itself of a potency (dunamis), as material, is thinghood. The being-at-work-staying-the-same of a potency as a potency is motion.