This third instinct lets the two opposing instincts (the sensuous and the formal instinct) act together. Even though they are each others total opposite, it is possible to play with them, let them be there at the same time.
As long as they are playing together, there has to be no conclusion on what is true and what is false. During the play, the mind can be physical and moral at the same time.
The instinct of play makes a communion possible between the two opposing instincts so that they can exist together without a final conclusion.