Text: Metaphysics is universal and is exclusively concerned with primary substance. ... And here we will have the science to study that which is just as that which is, both in its essence and in the properties which, just as a thing that is, it has. ... The entire preoccupation of the physicist is with things that contain within themselves a principle of movement and rest. ... There must then be a principle of such a kind that its substance is activity. (Aristotle, 340BC)

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