krey-
“to sieve, to separate”sieve, separate, judge
Root for sifting/separating, yielding Latin cernere (to separate), Greek krinein, English riddle.
Discussion
The Proto-Indo-European root *krey- meant "to sieve, to separate, to distinguish." The suffixed form *ḱrey-sis- is treated separately. Latin cernere, "to sift, to separate, to perceive," embodies the full arc: to perceive is to sift experience. Its compounds pervade English: discern (to sift apart), concern (to sift together), certain (sifted and settled), secret (separated away), and decree (to sift down). Crime descends from Latin crīmen, originally "judgment." The Germanic branch preserved the concrete meaning: English riddle (the coarse sieve) descends directly from *krey- through Proto-Germanic *hridlō. This makes the farmyard riddle and the Greek philosophical crisis cognates, separated by three thousand years of metaphorical development but united in the image of separating what passes through from what does not. The journey of *krey- from the threshing floor to the courtroom to the hospital bedside remains one of the most instructive examples of how Indo-European abstraction works: not by inventing new concepts, but by applying old physical operations to new domains.
Notes
Pokorny 945-946. English crime, crisis, critic, certain, decree, secret, riddle.