“There was a whole language that I could never make function for myself in relationship to painting,” said the artist Robert Rauschenberg, “and that was attitudes like tortured, struggle, pain.” He also said he wanted to work “in the gap between art and life.” In Rauschenberg’s “combines,” collages, and convergences that sense of limbo is confident, energized, inevitable. Fifteen years of freedom, here on view. —L.J.