All things happen by virtue of necessity.

By convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention colour is colour. But in reality there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.

I would rather discover one scientific fact than become King of Persia.

The first principles of the universe are atoms and empty space. Everything else is merely thought to exist. The worlds are unlimited. They come into being and perish. Nothing can come into being from that which is not nor pass away into that which is not. Further, the atoms are unlimited in size and number, and they are borne along in the whole universe in a vortex, and thereby generate all composite things—-fire, water, air, earth. For even these are conglomerations of given atoms. And it is because of their solidarity that these atoms are impassive and unalterable. The sun and the moon have been composed of such smooth and spherical masses [i.e. atoms], and so also the soul, which is identical with reason.

These differences, they say, are three: shape, arrangement, and position; because they hold that what is differs only in contour, inter-contact, inclination.

Anaximenes and Anaxagoras and Democritus say that its [the earth's] flatness is responsible for it staying still: for it does not cut the air beneath but covers it like a lid, which flat bodies evidently do: for they are hard to move even for the winds, on account of their resistance.

Mock on, mock on, Voltaire, Rousseau!
Mock on, mock on: 'Tis all in vain!
You throw the sand against the wind,
And the wind blows it back again.
And every sand becomes a gem
Reflected in the beams divine;
Blown back they blind the mocking eye,
But still in Israel's paths they shine.
The atoms of Democritus
And Newton's particles of light
Are sands upon the Red Sea shore,
Where Israel's tents do shine so bright.

Democritus sometimes does away with what appears to the senses, and says that none of these appears according to truth but only according to opinion: the truth in real things is that there are atoms and void. 'By convention sweet', he says, 'by convention bitter, by convention hot, by convention cold, by convention colour: but in reality atoms and void.'

'By convention there is color, by convention sweetness, by convention bitterness, but in reality there are atoms and the void,' announced Democritus. The universe consists only of atoms and the void; all else is opinion and illusion. If the soul exists, it also consists of atoms.