Book V
The focus of Book V is on 'change', which, according to Aristotle can occur in one of three senses: 1) Accidentally; 2) Partially (something belonging to the object changes or moves); and 3) Directly (the thing itself moves or changes). Change is always "from something to something". 'Coming to be' (change from nothing to something) or 'perishing' (change from something to nothing) cannot be considered true instances of change according to Aristotle because that which "is not" cannot possibly be in motion. Motion is therefore always from "subject to subject" and never from subject to non-subject (or vis versa) and can be classified in three different ways: 1) Qualitative; 2) Quantitative; 3) Local. Qualitative motion is also called alteration from one contrary to the other. Quantitative motion involves increase or decrease between two contraries. Local motion is another way to say 'locomotion'.
Book VI
In this Book, Aristotle contends that everything that changes, such as magnitude, time and motion, is continuious and "divisible into divisibles that are infinitely divisible." Within time, however, there is one thing that is indivisible: the present. The 'present' is a boundary or limit between the past and the future and is therefore impossible to divide. A good chunk of this chapter is taken up with refutations of Zeno's famous paradoxes using the principles that have been developed in the Physics up to this point. Both Aristotle and Zeno agree (contra the Atomists) that space and time are continuous and divisible, but whereas Zeno's paradoxes presuppose the existance of 'actual' infinities, Aristotle avoids the trap with his inriguing concept of 'potential' infinities.
Book VII
Book VII has some fascinating theological undertones which are later developed at greater length in the Metaphysics. The maxim of this Book is: "Everything that is in motion must be moved by something." But this immediately leads us right into the vexing problem of infinite regress which necessarily leads to a number of philosophical absurdities. The conclusion: "there must be some first movent (mover)."
Book VIII
According to Aristotle, there are two possible candidates for the first cause of all motion and change. It could either be a self-moving mover (like an animal) or it could an unmoved mover. In order to avoid the problem of infinite regress and a first cause that is neither eternal nor continuous, he concludes that the first cause must be an eternal, unmoved mover. This book contains a discussion on the kind of motion that such a first cause would produce, which in Aristotle's view, must be rotational or circular locomotion since this is the only form of motion which is both eternal and continuous. In Aristotle's scheme, it would appear that the unmoved mover causes the circular motion of the heavenly spheres, and this motion, in turn, is the cause of all other kinds of motion and change.
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