 As well as studies designed to elicit preferences, there are empirically motivated theories that purport to explain them. Among the earliest is Wundt’s (1874) suggestion that we judge a form pleasing to the extent that the eye finds it easy to follow the contour. Recent work generalises this thought: there is said to be a tendency for stimuli to be experienced positively when our perceptual or cognitive grasp on them comes easily (Reber, Schwarz, &amp; Winkielman 2004). This idea of processing fluency is not limited to the aesthetic domain; we generally find a proposition more believable, apparently, if it is expressed in rhyme or in an easy to read font and this is said to be because these things increase fluency (Reber &amp; Schwarz 1999; McGlone &amp; Tofighbakhsh 2000). So aesthetic and fluent phenomena are not coextensive, and no reduction of the one to the other is possible. The most that can be said (and this is not insignificant) is that certain kinds of fluency underpin experiences of aesthetic pleasure and displeasure, symmetry offering a plausible example; for comments on the significance of such research into underlying mechanisms see  Section 4  below.