Coherent
Etymology
From Latin "cohaerere" (to stick together, cling) — "com-" (together) plus "haerere" (to stick, cling), the same root behind adhere and hesitate (to be stuck). Coherence is literally the parts sticking to one another.
adjective · /koh-HEER-unt/
Having parts that fit together without contradiction into a connected whole.
What it names
Use it to praise an argument or account whose pieces hang together — while remembering that hanging together is not the same as being true.
Example
The conspiracy theory was internally coherent — every part supported every other — and completely detached from reality.
Related idea
Coherence is not correspondence: a story can be perfectly self-consistent yet match nothing in the world. This is the classic split in theories of truth — a good lie is coherent; a true account also corresponds to the facts.
adjective · /koh-HEER-unt/
In physics, describing waves that keep a constant phase relationship, as in laser light.
What it names
waves oscillating in step
Example
A laser produces coherent light, which is why its beam stays tight.
Related idea
The parts ‘hold together’ as in the logical sense — here in step rather than in argument.