ABSTRACT: Seeking to identify the common and distinguishing attributes of effects one might call "aesthetic," I examined hundreds of examples in music, visual arts, poetry, literature, humor, performance arts, architecture, science, mathematics, games, and other disciplines. I observed that all involve quasi-emotional reactions to stimuli that are composites of multiple elements that ordinarily do not occur together and whose interaction, when appropriately potentiated, is transformative-different in kind from the effects of the separate constituent elements. Such effects, termed synergetic, can evoke surprise-tinged emotional responses. Aesthetic reactions, unlike many other kinds of emotional reactions, are never evoked by biologically urgent action-demanding events, such as threats or opportunities. The examined effects were created by various concept manipulation devices: class expansion, identification of new relations, repetition, symmetry, parsimony, and emotional displays for the audience to mirror (I identified a total of 16 such devices). The effects would occur only for individuals with the necessary priming, in circumstances that include effective potentiating factors. Synergetic stimuli that evoke aesthetic responses tend to be reinforcing, via mechanisms related to their biological utility during our evolution. I offer a theory as to how aesthetics may have evolved from its primordial pre-aesthetic roots, with examples of how consideration of those roots often explains aesthetic and related effects. The article suggests that aesthetic phenomena are a special case of a more pervasive aspect of behavior and proposes research approaches involving laboratory models and fMRI technology.