G.K. Chesterton quote

The quote is "When people stop believing in God the problem is not that they believe in nothing, it is that they'll believe in anything."

I found the source for this quote near the bottom of the Wikiquote page for G.K. Chesterton, under the header, "Misattributed".

Wikiquote Chesterton page

They say:

When people stop believing in God, they don’t believe in nothing — they believe in anything.

* This quotation actually comes from page 211 of Emile Cammaerts' book The Laughing Prophets (1937) in which he quotes Chesterton as having Father Brown say, in "The Oracle of the Dog" (1923): "It's the first effect of not believing in God that you lose your common sense." Cammaerts then interposes his own analysis between further quotes from Father Brown: "'It's drowning all your old rationalism and scepticism, it's coming in like a sea; and the name of it is superstition.' The first effect of not believing in God is to believe in anything: 'And a dog is an omen and a cat is a mystery.'" Note that the remark about believing in anything is outside the quotation marks — it is Cammaerts. The American Chesterton Society has explained the origin of the phrase.

See the Chesterton Society's explanation of this.