adj
clever, bright, smart, brilliant, quick, alert, quick-witted, sharp, acute, discerning, perceptive, knowing, knowledgeable, well-informed, thinking, educated, rational, sensible formal perspicacious, sagacious
(colloq.) brainy, quick on the uptake, no flies on someone, knowing a thing or two, knowing how many beans make five, using your loaf, all there