sarcu -sa'u- gismu

x1 (abstract) is necessary/required for continuing state/process x2 under conditions x3.

Also factually necessary, necessity, prerequisite, condition, precondition. See also cmavo list sau, nitcu.

In definition:

sau
sarcu modal, 1st place requiring ...
sesau (comp!)
sarcu modal, 2nd place (process) necessarily; necessary for ...
tesau (comp!)
sarcu modal, 3rd place (conditions 2) necessarily; necessarily under ...

In notes:

nitcu
x1 needs/requires/is dependent on/[wants] necessity x2 for purpose/action/stage of process x3.
bazyjvesa'u
x1 is a necessary and sufficient condition for x2 to happen
bazysa'u
x1 is a necessary and sufficient condition for x2 to happen
faurbanzu
x1 (nu) is a sufficient condition/is enough for x2 (nu) to happen
pavmombesy'utka
x1 is path-connected to x2 via the male-only first-born progeny/primogeniture relation; x1 is the first-born son of the first-born son of ... the first-born son of x2, connected by a graph-path passing through intermediate relations/steps (successive first-born sons) x3 (ce'o; ordered list).
pavmompazy'utka
x1 is path-connected to x2 via the (non-gendered/absolute) first-born progeny/primogeniture relation; x1 is the first-born offspring of the first-born offspring of ... the first-born offspring of x2, connected by a graph-path passing through intermediate relations/steps (successive first-born offspring) x3 (ce'o; ordered list), "first" being according to ordering rule x4 (default, as used in this definition: chronological order of birth; restrictions on legitimacy etc. may also be included here).
pavmomtixy'utka
x1 is path-connected to x2 via the female-only first-born progeny/primogeniture relation; x1 is the first-born daughter of the first-born daughter of ... the first-born daughter of x2, connected by a graph-path passing through intermediate relations/steps (successive first-born daughters) x3 (ce'o; ordered list).
selsa'u
x1 (event) requires / depends on x2 (event/proposition)
eilga
x1 (du'u/nu) should (moral obligation) be true/happen by standard x2
samyuan
name: "Someone", aka "the god of lazy people", used when the speaker is pushing responsibility to someone else unspecified