IV

[from Wikipedia...]
Four rules : addition, subtraction, multiplication, division.
Greek classical elements (fire, air, water, earth).
Four seasons : spring, summer, autumn, winter.
Four parts of a day : night, morning, afternoon, evening.
Four cardinal directions : north, south, east, west.
Four horsemen of the Apocalypse : war, famine, pestilence, death.
Four suits of playing cards : hearts, diamonds, clubs, spades.
The number of tines of most forks.
Noble Truths in the Buddhist faith.
There are four human blood groups.
There are four basic states of matter: solid, liquid, gas, and plasma.