Because there are no fours.
He raped me ... he fondled me, he put me on all fours, and had sex with me,
The institution of taxation rests foursquare on the axiom that somebody must rule somebody else.
The only intelligent way to discuss politics is on all fours.
Nearly everything in life goes in threes and fours.
She's a twosome, she's a foursome, if she'd lose some, I would like her more some.
And so it continued all day, wynde after wynde, From a room beyond came the whistle of a teakettle. Now, you really must join me. I've some marvelous Darjeeling, and some delicious petit fours a friend of mine gave me for Christmas.