A cryptic question with a simple, clever answer. Often, a riddle is presented as a short poem, whose question "What am I?" is implied. The poem "Humpty Dumpty" is an example of such a riddle, whose answer is "egg".
IF As Riddle
In Twisty Little Passages (2003), Nick Montfort explores the similarities between the riddle - an ancient poetic tradition - and IF. While Montfort does not argue that the comparison is exact, he does consider the riddle an ancestor of IF, and that many of the elements of a good riddle are strongly analagous to the elements of a good piece of IF. Rather than dismissing puzzles as antagonistic to IF's literary qualities, this approach treats them as essential to the literary treatment of an IF work.