If there is a law that pick-pockets shall go to prison, it implies that there is an imaginable mental connection between the idea of prison and the idea of picking pockets.

And we know what the idea is.

We can say why we take liberty from a man who takes liberties.

But we cannot say why an egg can turn into a chicken any more than we can say why a bear could turn into a fairy prince.

As _ideas_, the egg and the chicken are further off each other than the bear and the prince; for no egg in itself suggests a chicken, whereas some princes do suggest bears.