pos

The root pos goes back to one of the most productive verbs in Latin: pōnere, meaning simply 'to place, to put, to set down.' A Roman farmer would pōnere a stone on a wall; a senator would pōnere a question before the assembly. The verb's past participle was positus — and this split is the key to the whole family. In English the family shows up as pose, pon, pos, posit, and position. They look different, but every one of them means the same thing underneath: to put something somewhere. (Strictly speaking, the -pose verbs came through French poser, from Late Latin pausāre, 'to stop, set down,' which merged with pōnere in meaning — but the sense they carry is pōnere's.)

What makes this root so rewarding is that the prefix tells you exactly where the thing is being put. Hold the idea of 'placing' constant, and let the prefix swing the direction:

- com- (together) + pose → compose: place parts together to make a whole — a song, an essay, a committee.
- ex- (out) + pose → expose: place something out in the open — reveal it, or leave it unprotected.
- de- (down) + posit → deposit: place money down in a bank, or let sediment settle down in layers.
- im- (on, upon) + pose → impose: place a rule or burden down onto someone.
- op- (against) + pose → oppose: place yourself against someone — stand opposite them in a fight.
- pro- (forward, before) + pose → propose: place an idea forward for others to consider.
- sup- (under) + pose → suppose: place an assumption underneath your reasoning, as a foundation.
- trans- (across) + pose → transpose: place things across each other — swap their order.
- inter- (between) + pose → interpose: place something in between.
- dis- (apart) + pose → dispose: place things apart in order — arrange them — or place them away, get rid of them.
- juxta- (beside) + pose → juxtapose: place two things side by side to compare them.

The three surface shapes can trip learners up, so it helps to file them mentally:

- pose / pos appears in the plain verbs: compose, expose, impose, oppose, propose, dispose.
- pon appears mostly in the -ent agent words and in postpone: component, opponent, proponent, exponent, postpone.
- posit / position appears in the noun and adjective branch: position, positive, opposite, deposit, composite, proposition.

A couple of members wander a little. Positive originally meant 'firmly set down, established' — a positive rule was one that had been formally laid down — and from 'definitely settled' it grew into 'certain,' and from there into the warm modern sense of 'optimistic, good.' Purpose hides the root behind a worn-down spelling: pur- is just a French-flavored form of pro- (forward), so a purpose is literally something you 'put forward' to aim at. Once you see pōnere underneath, the whole crowd of pos- words clicks into one family.