Kant summarized the physicotheological argument as follows:

1. Everywhere in the world there are clear signs of an ordering having occurred.

2. This ordering doesn't inhere in things but belongs to them, so to speak, only contingently.

3. Therefore, there must exist one or several knowing causes that have produced the world, not as a force that automatically determines its effect but as an intelligence that acts freely.

4. The unity of this cause can be inferred from the unity of the relationships between the various parts of the world, viewed as different pieces of a work of art.

This proof, for which Kant had special respect, has been subject to numerous objections. To be sure, no one doubts that the universe has a certain harmony. The first element of the proof is thus agreed upon by all philosophers.

But this isn't so with the second element. An entire school of thought, which can be traced back to Democritus, seeks to explain this order without invoking the notion of finality. But it's in the work of Epicurus that, for the first time, the problem is neatly stated and completely resolved. In his view, the harmony we see in the world is due neither to an ordering intelligence nor to scientific necessity but simply to chance. Atoms are endowed with freedom, so the forms of the bodies they make up are necessarily contingent. If atoms are combined to form the world as it is, the cause is chance alone.