Adam Clarke on Ecclesiastes 1:17

To know madness and folly - הוללות ושכלות holloth vesichluth. Παραβολας και επιστημην, "Parables and science." - Septuagint. So the Syriac; nearly so the Arabic. "What were error and foolishness." - Coverdale. Perhaps gayety and sobriety may be the better meaning for these two difficult words. I can scarcely think they are taken in that bad sense in which our translation exhibits them. "I tried pleasure in all its forms; and sobriety and self-abnegation to their utmost extent." Choheleth paraphrases, "Even fools and madmen taught me rules."