[Footnote 787: ][ (return) ] Lucretius, "On the Nature of Things," bk. i.
[Footnote 789: ][ (return) ] Diogenes Laertius, "Lives of the Philosophers," bk. x. ch. xxiv.
The two great principles of nature are a vacuum, and a plenum. The plenum is body, or tangible nature; the vacuum is space, or intangible nature. "We know by the evidences of the senses (which are our only rule of reasoning) that bodies have a real existence, and we infer from the evidence of the senses that the vacuum has a real existence; for if space have no real existence, there would be nothing in which bodies can move, as we see they really do move. Let us add to this reflection that one can not conceive, either in virtue of perception, or of any analogy founded on perception, any general quality peculiar to all beings, which is not either an attribute, or an accident, of the body or of the vacuum." [790]
Of bodies some are "combinations"--concrete bodies--and some are primordial "elements," out of which combinations are formed. These primordial elements, out of which the universe is generated, are "atoms" (ἄτοµοι). These atoms are "the first principles" and "seeds" of all things. [791] They are "infinite in number," and, as their name implies, they are "infrangible" "unchangeable" and "indestructible." [792] Matter is, therefore, not infinitely divisible; there must be a point at which division ends. [793]
The only qualities of atoms are form, magnitude, and density. All the other sensible qualities of matter--the secondary qualities-- as color, odor, sweetness, bitterness, etc.--are necessarily inherent in form. All secondary qualities are changeable, but the primary atoms are unchangeable; "for in the dissolution of combined bodies there must be something solid and indestructible, of such a kind that it will not change, either into what does not exist, or out of what does not exist, but the change results from a simple displacement of parts, which is the most usual case, or from an addition or subtraction of particles." [794]
[Footnote 790: ][ (return) ] Diogenes Laertius, "Lives of the Philosophers," bk. x. ch. xxiv.
[Footnote 791: ][ (return) ] Id., ib., bk. x. ch. xxv.
[Footnote 792: ][ (return) ] Id., ib., bk. x. ch. xxiv.
[Footnote 793: ][ (return) ] Id., ib.; Lucretius, "On the Nature of Things," bk. i. l. 616-620.