Four cardinal directions

North, south, west, east — four cardinal directions organize space. Four elements (fire, water, earth, air), four seasons, four phases of the Moon — nature is organized around the number four.

In Japanese and Chinese, the word for 'four' (四, shi/sì) sounds like the word for 'death'. This phenomenon is called tetraphobia. Many Asian buildings lack a 4th floor, just as European buildings often lack a 13th.

Solid, liquid, gaseous and plasma — the four fundamental states of matter studied in physics and chemistry.