Breakdown of Wychodzę z założenia, że on jest uczciwym ekspertem.
być
to be
on
he / it (m)
że
that
z
from (+ Genitive)
Questions & Answers about Wychodzę z założenia, że on jest uczciwym ekspertem.
Why does this sentence use the verb wychodzić (to go out/leave) to mean "I start from"?
This is a common abstract use of a verb of motion. Just as you physically "walk out" of a starting point, in Polish you logically "proceed out of" an assumption. The phrase wychodzić z założenia is a fixed idiom meaning "to start from the assumption" or simply "to operate on the premise".
Since this is an abstract idiom, why use the imperfective wychodzę? Could I use the perfective wyjdę?
Holding a general assumption is treated as an ongoing state of mind, which is why we use the imperfective wychodzić here. If you were to use the perfective wyjdę, it would change the meaning to a specific, one-time future action: "I will make the assumption" or "I will start from the assumption (this one time)."
In English we say "start from an assumption". Why does Polish use the preposition z instead of od?
In Polish, the idiom is literally to step "out of" an assumption. The preposition z (out of) pairs naturally with the prefix wy- (out) in the verb wychodzić. When a verb begins with the wy- prefix, it very frequently requires z to complete the logic of the motion, even when used abstractly.
Could I just use the verb zakładać (to assume) instead of this entire phrase?