Play and Playfulness:

"Part of our thesis in this book [Play, Playfulness, Creativity and Innovation; Bateson & Martin] rests on the distinction we have drawn between observable play behaviour and an underlying mood state that we refer to as playfulness. Play behaviour may or may not be playful. Playfulness is a particular positive mood state that may (or may not) be manifested in observable behaviour. Playfulness facilitates and accompanies playful play, a subset of broadly defined play, which is distinct from what happens in formal games, theatrical performances and so forth. Play and playfulness do overlap, but we believe the distinction is important because some aspects of play behaviour are not playful, particularly when they start to merge into overt competition or aggression. Aspects of what many biologists and psychologists would subsume under the general heading of play may be driven by frustration or striving for social dominance. An encounter that starts off in a way that is described as playful may degenerate into overt aggression, when the lightness of mood associated with other aspects of play seems to be lacking. Conversely, playful individuals are not necessarily playing, even though they are in a playful mood."