A cause is a relation of alteration (movement) between two things.

Put a match unlight upon your hand. It will have no effect on your organism. There is here then no proper cause — in the mere relation of contiguity.

The day comes after the night, and the night after the day but, etc.

Cause then does not consist, of necessity, in a relation of succession.

Now, if you drink, for instance, prussic acid, you will die. The prussic acid was the direct cause of your death. There are here contiguity, succession, but as we have seen, cause has not its essence in these. What then is here more? There is here an alteration produced.

Run a billiard ball against another: this last, when struck will move away. Here are contiguity, succession, and what more? A movement, that is to say a kind of an alteration. We now can perceive the characteristic of Cause. [...]