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These arguments make it plain that every body has its natural movement,
which is not constrained or contrary to its nature. We go on to show that there
are certain bodies whose necessary impetus is that of weight and lightness. Of
necessity, we assert, they must move, and a moved thing which has no natural
impetus cannot move either towards or away from the centre. Suppose a body
A without weight, and a body B endowed with weight. Suppose the
weightless body to move the distance CD, while B in the same time moves
the distance CE, which will be greater since the heavy thing must move
further. Let the heavy body then be divided in the proportion CE: CD (for
there is no reason why a part of B should not stand in this relation to the
whole). Now if the whole moves the whole distance CE, the part must in the
same time move the distance CD. A weightless body, therefore, and one
which has weight will move the same distance, which is impossible. And the
same argument would fit the case of lightness. Again, a body which is in
motion but has neither weight nor lightness, must be moved by constraint, and
must continue its constrained movement infinitely. For there will be a force
which moves it, and the smaller and lighter a body is the further will a given
force move it. Now let A, the weightless body, be moved the distance CE, and
B, which has weight, be moved in the same time the distance CD. Dividing
the heavy body in the proportion CE:CD, we subtract from the heavy body a
part which will in the same time move the distance CE, since the whole
moved CD: for the relative speeds of the two bodies will be in inverse ratio to
their respective sizes. Thus the weightless body will move the same distance
as the heavy in the same time. But this is impossible. Hence, since the motion
of the weightless body will cover a greater distance than any that is suggested,
it will continue infinitely. It is therefore obvious that every body must have a
definite weight or lightness. But since ‘nature’ means a source of movement
within the thing itself, while a force is a source of movement in something
other than it or in itself qua other, and since movement is always due either to
nature or to constraint, movement which is natural, as downward movement is
to a stone, will be merely accelerated by an external force, while an unnatural
movement will be due to the force alone. In either case the air is as it were
instrumental to the force. For air is both light and heavy, and thus qua light
produces upward motion, being propelled and set in motion by the force, and
qua heavy produces a downward motion. In either case the force transmits the
movement to the body by first, as it were, impregnating the air. That is why a
body moved by constraint continues to move when that which gave the
impulse ceases to accompany it. Otherwise, i.e. if the air were not endowed
with this function, constrained movement would be impossible. And the
natural movement of a body may be helped on in the same way. This
discussion suffices to show (1) that all bodies are either light or heavy, and (2)
how unnatural movement takes place.
629
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book The Complete Aristotle"
The Complete Aristotle
- Title
- The Complete Aristotle
- Author
- Aristotle
- Date
- ~322 B.C.
- Language
- English
- License
- PD
- Size
- 21.0 x 29.7 cm
- Pages
- 2328
- Keywords
- Philosophy, Antique, Philosophie, Antike, Dialogues, Metaphysik, Metaphysics, Ideologie, Ideology, Englisch
- Categories
- Geisteswissenschaften
- International
Table of contents
- Part 1; Logic (Organon) 3
- Categories 4
- On Interpretation 34
- Prior Analytics, Book I 56
- Prior Analytics, Book II 113
- Posterior Analytics, Book I 149
- Posterior Analytics, Book II 193
- Topics, Book I 218
- Topics, Book II 221
- Topics, Book III 237
- Topics, Book IV 248
- Topics, Book V 266
- Topics, Book VI 291
- Topics, Book VII 317
- Topics, Book VIII 326
- On Sophistical Refutations 348
- Part 2; Universal Physics 396
- Physics, Book I 397
- Physics, Book II 415
- Physics, Book III 432
- Physics, Book IV 449
- Physics, Book V 481
- Physics, Book VI 496
- Physics, Book VII 519
- Physics, Book VIII 533
- On the Heavens, Book I 570
- On the Heavens, Book II 599
- On the Heavens, Book III 624
- On the Heavens, Book IV 640
- On Generation and Corruption, Book I 651
- On Generation and Corruption, Book II 685
- Meteorology, Book I 707
- Meteorology, Book II 733
- Meteorology, Book III 760
- Meteorology, Book IV 773
- Part 3; Human Physics 795
- On the Soul, Book I 796
- On the Soul, Book II 815
- On the Soul, Book III 840
- On Sense and the Sensible 861
- On Memory and Reminiscence 889
- On Sleep and Sleeplessness 899
- On Dreams 909
- On Prophesying by Dreams 918
- On Longevity and the Shortness of Life 923
- On Youth, Old Age, Life and Death, and Respiration 929
- Part 4; Animal Physics 952
- The History of Animals, Book I 953
- The History of Animals, Book II translated 977
- The History of Animals, Book III 1000
- The History of Animals, Book IV 1029
- The History of Animals, Book V 1056
- The History of Animals, Book VI 1094
- The History of Animals, Book VII 1135
- The History of Animals, Book VIII 1150
- The History of Animals, Book IX 1186
- On the Parts of Animals, Book I 1234
- On the Parts of Animals, Book II 1249
- On the Parts of Animals, Book III 1281
- On the Parts of Animals, Book IV 1311
- On the Motion of Animals 1351
- On the Gait of Animals 1363
- On the Generation of Animals, Book I 1381
- On the Generation of Animals, Book II 1412
- On the Generation of Animals, Book III 1444
- On the Generation of Animals, Book IV 1469
- On the Generation of Animals, Book V 1496
- Part 5; Metaphysics 1516
- Part 6; Ethics and Politics 1748
- Nicomachean Ethics, Book I 1749
- Nicomachean Ethics, Book II 1766
- Nicomachean Ethics, Book III 1779
- Nicomachean Ethics, Book IV 1799
- Nicomachean Ethics, Book V 1817
- Nicomachean Ethics, Book VI 1836
- Nicomachean Ethics, Book VII 1851
- Nicomachean Ethics, Book VIII 1872
- Nicomachean Ethics, Book IX 1890
- Nicomachean Ethics, Book X 1907
- Politics, Book I 1925
- Politics, Book II 1943
- Politics, Book III 1970
- Politics, Book IV 1997
- Politics, Book V 2023
- Politics, Book VI 2053
- Politics, Book VII 2065
- Politics, Book VIII 2091
- The Athenian Constitution 2102
- Part 7; Aesthetic Writings 2156