pos

com- (together) + pose (place) = 'place parts together.' From this one image grow three everyday senses: to make up a whole (water is composed of hydrogen and oxygen), to create art by arranging parts (compose a symphony, an email), and — most surprisingly — to calm yourself (compose yourself), where you 'put your scattered feelings back together' into order. The thread is always assembly: gathering pieces into a settled arrangement.

ex- (out) + pose (place) = 'place out in the open.' Take something hidden and set it where everyone can see it: expose a scandal, expose the truth. The same act of removing cover gives the darker sense of vulnerability — skin exposed to the sun, a soldier exposed to fire. And in photography, an 'exposure' is literally the film being placed out to the light.

op- (a form of ob-, 'against') + pose (place) = 'place against.' To oppose is to set yourself directly in front of and against something. The same root gives opposite (the thing placed across from you) and opponent (the one placed against you in a contest). Picture two armies lined up facing each other — that is the literal 'placing against.'

The family's most surprising journey. From positus ('placed, set down'), a 'positive' law originally just meant one that had been formally laid down by an authority — firmly fixed rather than natural. 'Firmly fixed' became 'certain' (I'm positive he's lying), and 'certain/affirmed' drifted into today's warm sense of 'good, optimistic' (a positive attitude). Even the physics meaning — a positive charge — keeps the old idea of something definitely 'set' on one side.

de- (down) + posit (place) = 'place down.' You deposit money by putting it down into a bank for safekeeping; a river deposits silt by laying it down in layers. The noun also means the down payment you 'put down' to hold something. One root, one motion — setting something down to rest where it will stay.