number 4...

.


"The problem with putting two and two together is that sometimes you get four, and sometimes you get twenty-two."
Dashiell Hammett






four...
rules: addition, subtraction, multiplication, division...
greek classical elements (fire, air, water, earth)...
seasons: spring, summer, autumn, winter...
cardinal directions: north, south, east, west...
temperaments: sanguine, choleric, melancholic, phlegmatic...
humors: blood, yellow bile, black bile, phlegm...
cardinal virtues: justice, prudence, temperance, fortitude...
suits of playing cards: hearts, diamonds, clubs, spades...
(not forgetting the"Fab Four"...)


(well, you asked!?...)