Sharing the Moment
in contact improv, depth of engagement depends on mutual responsiveness rather than imposition of control.
In the most basic description, Contact Improvisation is a game where partners mutualy follow shared points of contact to discover what they're doing together. The more that partners allow themselves to follow what's happening - follow the course of their partner and of themselves, rather than leading - the more that the dance can be immediate and engaging.
Typical games have a number of more explicit rules, spelling out the play by narrowing the choices: "roll the ball down the alley", "take turns", "if you swing and fail to hit the ball three times, you're out", etc. More rules makes it simpler for players to find their way in, but limits the form of play. In particular, it limits the involvement of the players in developing what they're doing together as they go.
Enabling people to play together means creating a situation with common ground - shared activity within which they can connect. If the common ground is too restrictive, it overly limits choice - opportunities for invention and spontaneity. If it is too open, on the other hand, the players lack the basis to find one another, to mutually engage together.
Contact Improv's mutual following of a shared point of contact is elementary (but not necessarily simple :-) and open-ended. There is plenty of opportunity for personal discretion, but as in any form, that opportunity depends on a kind of commitment to the agreements - in this case, to collaborating, by following, rather than taking over and controlling, or withdrawing by not investing in the connection. Mutual following offers the richness of an inter-responsive dynamic.
It's revealing that a person can do Contact Improv solo. You can find rich dynamics in following the activity of your own body, engaging with gravity, momentum, and the intricate dynamics of your musculoskeletal self. That microcosm is present in multiples when engaging with a partner - following the contact point involves following your own internal activities, as much as those of your partner, as evidenced in the point. The magic that can arise is in being engaged, diversely, together, and that is what CI fosters.
Ultimately, CI Is An Opportunity to Play.
And with a musician:
Respecting Boundaries has guidelines for keeping choices open in the face of real-world complications.
What People Do At Jams describes the situation in contact improv's primary habitat.
See What Contact Improv Does for my take on how to learn CI