Four for some reason

Four cardinal directions: north, south, east, west
Four fundamental forces of nature: gravity, the strong nuclear force, the weak nuclear force, and the electromagnetic force
Four giant gas planets in the Solar system: Jupiter, Saturn, Uranus, Neptune
Four Greek classical elements: fire, air, water, earth
Four horsemen of the Apocalypse: war, famine, plague, death
Four human blood groups: A, B, O, AB
Four parts of a day: morning, afternoon, evening, night
Four rules: addition, subtraction, multiplication, division
Four seasons: spring, summer, autumn, winter
Four suits of playing cards: hearts, diamonds, clubs, spades
Four terrestrial planets in the Solar system: Mercury, Venus, Earth, Mars.


I'm listening to Joan Baez "Love Is Just A Four-Letter Word" from: The First 10 Years