The Atomists

1. The Atomists On change

2. Aristotle Again, even if it is quite impossible both for what does not exist to come into being and for what exists to perish, why should not some things nevetheless be generated and others eternal as Empedocles says? For he too, having admitted all this –namely that from what does not exist nothing can come into being, and for what exists to be destroyed is impossible and unaccomplishable— Nevertheless he says that some things are eternal while others come and have come into being from them. Aristotle, On Melissus

3. The Atomists Leucippus Democritus

4. Democritus Democritus thinks that the nature of eternal things consists in small substances, infinite in quantity, and for them he posits a place, distinct from them and infinite in extent. He calls place by the names ‘void’, ‘nothing’ and ‘infinite’; and each of the substance she calls ‘thing’, ‘solid’ and ‘being’. He thinks that he substances are so small that they escape our sense, and that they possess all sorts of forms and all sorts of shapes and differences in magnitude. From them, as from elements, he was able to generate and compound visible and perceptible bodies. The atoms struggle and are carried about the in the void because of their dissimilarities and other differences mentioned, and as they are carried about they collide and are bound together… up to the time when some stronger force reaches them from their environment and shakes them and scatters them apart. Aristotle, Fragment 208

5. Definitions • x is an improper part of y =df x = y. • x is a proper part of y =df x is a part of y and x ≠ y. • x is a mereological simple =df x has no proper parts. • x and y overlap =df there is some z such that z is a part of both x and y. • the xscompose y =df (i) each of the xs is a part of y and (ii) the xs overlap every part of y.

6. Democritus • Something is an atom if and only if it is a mereological simple. • The Atomist Doctrine: All that exists is either identical to, or composed of, mereological simples.

7. Parmenides’ Anti-Generation Argument • Necessarily, if something comes into existence, then either (a) it comes from nothing or (b) it comes from something else. • It is impossible that (a). • It is impossible that (b). • [So] It is impossible that something comes into existence.

8. The Argument for (3). • If (b) is possible, then it is possible for there to be an x and y such that x comes into existence from y, but y is not x. • If x comes into existence from y then y became x. • If y became x then y is x. • It is not possible for there to be an x and y such that y is x and y is not x. • It is not possible that (b).

9. Democritus’ Argument For Atomism There is a difficulty if one supposes that there is a body or magnitude which is divisible everywhere… suppose it to have been divided. What will be left? A magnitude? That is not possible; for then there will be something that has not been divided, but we supposed it divisible everywhere. But if there is to be no body or magnitude left and yet the division is to take place, it will either consist of points and its components will have no magnitude, or else they will be nothing at all so that what would come to be, and be composed, from nothing and the whole body would be nothing but an appearance. Aristotle, On Generation and Corruption

10. Democritus’ Argument For Atomism • If there is a composite object that is not composed of atoms, then that object could be divided infinitely many times. • If a composite object could be divided infinitely many times, then either (a) that object is composed of points, or else (b) that object is composed of nothing. • No composite object is composed of points. • No composite object is made up of nothing. • [So] Every composite objects is composed of atoms.

11. Definitions • x is composed of atomless gunk =df x has proper parts and all of x’s proper parts have proper parts.

12. Democritus’ Argument For Atomism • If there is a composite object that is not composed of atoms, then that object could be divided infinitely many times. • If a composite object could be divided infinitely many times, then either (a) that object is composed of points, or else (b) that object is composed of nothing. • No composite object is composed of points. • No composite object is made up of nothing. • [So] Every composite object is composed of atoms.