VB  discover, find, determine, evolve, learn, fix upon, pick up, find out, trace out, make out, hunt out, fish out, worm out, ferret out, root out, fathom, bring out, draw out, educe, elicit, bring to light, dig out, grub up, fish up, unearth, disinter, solve, resolve, elucidate, unriddle, unravel, unlock, crack, crack open, pick up, open the lock, find a clue, find clew a to, find the key to the riddle, interpret, disclose, trace, get at, hit it, have it, lay one's finger, lay one's hands upon, spot, get at the truth, arrive at the truth, put the saddle on the right horse, hit the right nail on the head, be near the truth, be warm, get warmer, burn, smoke, scent, sniff, catch a whiff of, smell a rat, open the eyes to, see through, see daylight, see in its true colors, see the cloven foot, detect, catch, catch tripping, pitch upon, fall upon, light upon, hit upon, stumble upon, pop upon, come across, come onto, meet with, meet up with, fall in with, recognize, realize, verify, make certain of, identify, Int, eureka!, aha!, I've got it!.

act upon, agreed upon, alight upon, bear down upon, bear upon, blunder upon, borne in upon, build upon, burst upon, chance upon, come upon, coming upon, comment upon, depend upon, descend upon, embark upon, encroach upon, enter upon, expanding upon, fall upon, fasten upon, fawn upon, feed upon, force upon, frown upon, gain upon, happen upon, hinge upon, hit upon, impose upon, insist upon, light upon, look down upon, look upon, marched upon, obtrude upon, pounce upon, presume upon, prevail upon, put upon, reflect upon, set upon, settle upon, spring upon, stumble, supervene upon, swoop down upon, touch upon, tread upon, upon, upon one's guard, visit upon, wear upon, weigh upon